Mimicking Lipton's Green Diet Iced Tea Citrus

I think this is going to be difficult to do without taste-testing, so you might have to learn to like green tea just a bit. ;)

First, after a quick search I found that another person who tried to tackle this problem ended up using crystallized lime powder (e.g., True Lime) to get to the intended result. It looks like these recipes use orange extract too, so that might be an additional purchase for you — it's usually in the baking aisle of a supermarket.

Assuming you wanted to try with the ingredients you have, this will be a lot of trial and error, but here's how I would approach it (with a notebook to write down everything I'm adding!):

Note: Watch tablespoons vs. teaspoons here, as they could make a big difference when making small adjustments.

Start with the tea

• I'm not sure what kind of green tea you bought, so I would start by making the tea using the powdered mix per the instructions and ratios on the package. For example, it looks like the Lipton green tea mix is 4 tablespoon:1 cup of water. There are 16 cups in a gallon, maybe experimenting with 1/2 gallon (8 cups water) at a time will give you a little margin for error without as much waste.
• You might try mixing a small amount of your powder with water first to make it a smooth paste before adding the rest of the water, which will help avoid grittiness of the powder (you could do this with any powder you add).
• When you taste this, you're tasting for the tea flavor: it should be earthy and bitter. If it tastes too weak, you need to up the powder, one teaspoon at a time. If it tastes just too strong, hold off adding water before you add other ingredients, as they might lessen it a bit. You can always add water, but you can't take it out. For you, I would shoot for too strong of a tea taste.

Add the citrus/acidity

• Next, I would work on the citrus/acid. When they say "natural flavors," it's possible they're using citrus oils, which come from the skin. (You can buy these at the store, too.) The citrus juice has a lot less of the flavor we would recognize as strongly lemon or lime. The acids will also give you a slight citrus flavor. Using what you've got, you might try using a bunch of citrus juice with a bit of the acid to supplement it, which might taste more "natural" in the end.
• Citrus juices: start by adding 2 tablespoons of lemon and maybe 1 tablespoon of lime juice per 1/2 gallon. If you do try getting orange extract, this is when I would add it 1/8 teaspoon at a time, since it is quite strong. Try incrementing by those amounts until you get the right citrus flavor. If the flavor is right but the tartness isn't there, move on to the acids.
• Acids: Your ascorbic acid and citric acid will more or less be doing the same job of adding tartness, with citric acid being a bit more sour. For your purposes, I'd only test one at a time. This will take a lot of experimenting, but I would only add 1/4 tsp of the acid a time until it tastes tart enough.

Add sweetener

• I don't personally use sugar substitutes, so I can't speak to how this works or tastes. The recipe linked at the top shows a ratio of 1 1/4 tsp (5 packets) per half gallon, so that seems as good a starting point as any.

If after all of this, it tastes like too much, you could add 1/2 cup of water at a time.

Here's this starting point written in a list, using your ingredients:

• 1/2 gallon green tea, following package instructions
• plus 2 tablespoons bottled lemon juice, more as needed
• plus 1 tablespoon bottled lime juice, more as needed
• plus 1/4 teaspoon ascorbic or citric acid, more as needed
• plus 1 1/4 teaspoon (5 packets) Equal, more as needed
• then add water to dilute as needed

Good luck! This is a really sweet thing that you're trying to do for your girlfriend and I hope you enjoy the process of experimenting — it would be a fun thing to share your process with her!