How long can eggs be unrefrigerated before becoming unsafe to eat?

I never refrigerate eggs. They are marked for room temperature storage in UK and perfectly safe up to (and after) the use by date. Three days should be no problem unless you live somewhere really hot.

The USDA, generally on the very safe but a bit paranoid end of the spectrum, says:

After eggs are refrigerated, they need to stay that way. A cold egg left out at room temperature can sweat, facilitating the movement of bacteria into the egg and increasing the growth of bacteria. Refrigerated eggs should not be left out more than 2 hours.

(They also say some very sad things about Easter egg hunts.)

So if you're being strict, three days would be way too long. In reality, you'd probably be okay. The chances of getting salmonella are definitely higher, but are presumably still small (though I can't say exactly how small, of course). Personally, given the price of a dozen eggs, I'd probably play it safe.

Another answer mentions that in the UK eggs are stored at room temperature. That's true in quite a lot of places, but I'm guessing that they've avoided the large temperature swing issue mentioned by the FDA, so if your friend's eggs were refrigerated in the store, the situation's not quite the same as in the UK.

In Italy eggs are usually sold in non refrigerated aisles, and they generally last no less than a couple of weeks. There is on this regard an EU regulation that more or less says what the american FDA is saying. It suggests, however, not to refrigerate eggs before sale, so that helps with bacteria and such.

I don't know whether eggs in the USA are sold refrigerated or not, but if they aren't, and your friend didn't put them in the refrigerator there is a good chance that they could be used without any problem.

Keep in mind, however, that salmonella bacterium is basically neutralized by high temperatures, so if she plans to bake cookies there shouldn't be any problem. According to USDA FSIS a temperature of 160F should be enough to neutralize the bacterium.

A bit of scientific references (bold mine):

Numbers of Salmonella enteritidis in the contents of naturally contaminated hens' eggs.

Over 5700 hens eggs from 15 flocks naturally infected with Salmonella enteritidis were examined individually for the presence of the organism in either egg contents or on shells. Thirty-two eggs (0.6%) were positive in the contents. In the majority, levels of contamination were low. Three eggs, however, were found to contain many thousands of cells. In eggs where it was possible to identify the site of contamination, the albumen was more frequently positive than the yolk. Storage at room temperature had no significant effect on the prevalence of salmonella-positive eggs but those held for more than 21 days were more likely (P less than 0.01) to be heavily contaminated. In batches of eggs where both shells and contents were examined, 1.1% were positive on the former site and 0.9% in the latter.

Contamination of egg shell and contents with Salmonella enteritidis: a review.

Salmonella enteritidis can contaminate the contents of clean, intact shell eggs as a result of infections of the reproductive tissue of laying hens. The principal site of infection would appear to be the upper oviduct. In egg contents the most important sites of contamination are either the outside of the vitelline membrane or the albumen surrounding it. In fresh eggs, only few salmonellas are present and as albumen is an iron-restricted environment, growth will only occur once storage-related changes to vitelline membrane permeability, which allow salmonellas to invade yolk contents, have taken place. When this happens high populations are achieved in both yolk contents and albumen. Some eggs from naturally infected hens have been found to contain large numbers of S. enteritidis. The rate of change in membrane permeability is temperature-dependent. In eggs stored at 20 degrees C, yolk invasion is uncommon until eggs have been stored for 3 weeks. In stimulated kitchen conditions where temperatures reached 30 degrees C, salmonellas could grow rapidly after a few days.

From Toward better control of Salmonella contamination by taking advantage of the egg's self-defense system: a review.

Storage Storage conditions present issues in contamination with focus on duration, temperature, and environmental hygiene. Different countries have different regulations. Storage limits for table eggs in the United Kingdom were 3 wk at 8 °C (Kinderlerer 1994), while in Israel 3 mo for refrigerated eggs and 16 d at room temperature (Lublin and Sela 2008). In many countries, eggs are required to be stored at low temperatures to restrict microbial growth. In Germany, legislation required that egg cooling be applied at 5 to 8 °C for 18 d maximum post lay (EFSA 2009). And in the United States, either shell eggs packed for consumers or eggs that receive a treatment from egg producers were required to be kept at 45 °F (7.2 °C) no later than 36 h after the eggs are laid during storage and transportation (FDA 2010). In this scenario, it is more advisable to apply low-temperature storage in order to minimize the possibility that eggs infected with?S.?Enteritidis are transmitted to humans. This recommendation is supported by the study of Gast and Holt (2000), which showed that low temperatures were more effective for controlling?S.?Enteritidis multiplication in the yolk when high concentration of?S.?Enteritidis was artificially introduced into egg contents. (Gast and Holt 2000). On the other hand, low temperature can slow down the process of penetration (Chousalkar and others2010). However, Kang and others (2006) suggested that it is preferable to store eggs at 37 °C for a certain period of time first, instead of 4 °C directly, to allow the endogenous bactericidal activity of egg albumen to kill the contaminating?S.?Enteritidis. This reasoning is valid especially when most eggs are infected through trans-shell contamination. While in the case of vertical transmission, this application awaits more research. Further studies show that, although low preservation temperature for table eggs will limit the multiplication of?Salmonella, it does not reduce the existing?Salmonella?concentration. It may indeed prolong the survival of?Salmonella?because?Salmonella?may be increased by low storage temperature (Baker and Balch 1962; Radkowski 2002; Messens and others 2006) and reduced with higher temperature (Rizk and others 1996).

On a side note, they also tackle the point of washing eggs

The use of egg washing is a continuous debate despite its broad commercial application. Current concerns focus on whether egg washing increases the internal microbial load. Within the European Union, egg washing is prohibited except in Sweden and parts of the Netherlands. The reason offered is that egg-washing procedures may damage the quality of the cuticle enhancing the opportunity for bacterial invasion (Peebles and Brake 1986; Bialka and others 2004; EFSA 2005). Factors related to cuticle damage caused by egg washing include presence of water on the eggshell, presence of iron in the wash water, physical brushing damage, and high pressure (Commission of European Communities, 2003). These are the reasons that class A eggs for human consumption are not eligible for the practice of egg washing by European Union legislation and eggs will be downgraded if any forms of disinfection are used. However, this reasoning is at odds with research that showed the washing procedure did not appear to affect the incidence of open pores and the overall cuticle quality. Meanwhile, it was also indicated that brown eggs in general were of better quality in terms of their cuticle scores than the white eggs when 4 standards, such as mechanical damage, debris, open pores, and cuticle coverage, were considered (Messens 2009). And the use of egg washing is yet authorized in Canada, America, Japan, Australia, Russia, and Mexico for the reason that egg washing can reduce the total microbial load on the surface of sanitized eggs by approximately 2 to above 5 log units (Hutchison and others 2004; Rodríguez Romo 2004).
Given the controversy on the advantages and disadvantages of egg washing, other procedures are being evaluated.

Mother Earth News ran a pretty comprehensive test of egg storage methods back in 1977. The room-temperature eggs lasted well over a month before starting to degrade.