Is there an acid substitute for cirtrus or vinegar?

Love the tamarind paste idea. I sometimes use yogurt in dressings along with or instead of acids. In addition to its bright flavor, I find that it creates dressings that are more refreshing than other egg or cheese-based creamy dressings.

Vermouth, too. Tomatoes, definitely. Also, pomegranate molasses and tamarind paste are excellent for an acidic element.

Wine is always an option!! Depending on what you are planning on using it for, buttermilk is acidic as well. I also believe tomatoes are, but that's only because I've been told not to cook them in my cast iron, because the acid will hurt my seasoning!

Again, depends on what you are planning to do with it. I hope she's not allergic to wine, that would be horrible!! :)

I'm not sure about the issues with allergies, but look into verjus and sumac as options.