Can I use a rectangular ceramic pan instead of enameled cast iron to bake bread without losing the nice crust?

Doesn't matter; you cannot use a ceramic pan with that baking technique.

If you heat the ceramic pan to 500F and then add the wet dough, it is likely to crack, and possibly even explode. Same goes for glass. Ceramic pan maker Emile Henry says:

Never preheat your ceramic baking dish dry, always add cooking oil or some type of liquid to the dish.

You should, instead, find a covered cast-iron loaf pan, such as the one by Staub, or a different baking technique, such as the traditional cold-oven cloche technique.

In a very similar position to you, I switched to an old-fashioned sheet steel loaf tin. The method is a little different

I line the tin with reusable non stick liner, and prove the dough in the tin (overnight in the fridge, taking it out an hour before baking, though 2-3 hours would be better). I bake uncovered, and when I put the loaf into the oven I add boiling water to a preheated pan on the oven floor.

The side crust is a bit easier for slicing this way, and overall the loaf is better for sandwiches. Proving in another container and preheating the loaf tin didn't work for me - shaping the loaf and placing it in the tin was the problem.

There are two good answers here at this point, but I'll just add a little more about why your wife's method works. It is not just heat conductivity. First, cast iron does store a ton a energy as it is being pre-heated in the oven. When the bread is first placed in the pan, that stored heat is transferred to the dough, helping to create the bottom crust.

Secondly, however, you cover the pan, creating a very moist environment, as moisture from the dough is turned to steam and trapped. In a way, this recreates the effect of a steam injection oven found in artisan bakeries. This steam generation and capture is difficult to recreate in a home oven, even with various hacks that home bakers uses.

That said, a sandwich loaf is usually baked differently, as pointed out by @FuzzyChef. As a follow-up to his answer, you might also search "cast iron bread cloche" to find other options. Most are not rectangular, but a more elongated shape might be more to your liking.

While the pan material does have an impact, when using this method, the cover on the Dutch oven is critical. That is hard to reproduce. I have seen success, baking a boule, with a sheet pan and a stainless steel prep bowl as an alternate. That might work as an experiment, if you have a large enough prep bowl that you can place over a loaf pan. Alternately, why not try a heavy loaf pan with some of the more common moisture hacks (spray bottle...water pan in bottom of oven...etc.)? As @Chris H points out, the crust won't be as thick, but maybe you will enjoy the texture for sandwiches.