Tahini substitute?

Thinned natural peanut butter (not the kind with sugar added) could work.

Almond butter or another nut butter may work. Tahini is pretty much just crushed sesame seeds and oil, and it has a very mild nutty flavour and is slightly pasty or chalky on the tongue, I’ve never come across anything that really replaces it too well.

For matching with falafel, I would say don’t bother with a tahini substitute and go straight for hummus, preferably a very tasteful one (I just sampled a jalapeno hummus that would be great for you). You could also make up a garlic sauce.

Hummus. Mmmm. Or you could try tzatziki, which a yogurt -based sauce. I’ve linked to Alton Brown’s recipe; just scroll to the bottom of the page.

Hummus is made with tahini, folks. that would not be good for her. I think the tzatziki is a great idea.

Yes, but you can make your own hummus without any tahini. It’s very easy to make if you have a food processor.