Stay as far away from baquacil as you can.
99% of the time, people who think they are allergic to chlorine are actually just allergic to the byproducts of inadequate chlorine breaking down waste in the water. The amount of active chlorine in a TFP pool is less than the chlorine found in tap water. If your friend can’t take a shower because of chlorine in the water then maybe it’s good to look at chlorine alternatives.
If you start out with chlorine and follow the TFP recommendations, your friend can try it out and see how it works out. If they really are allergic to chlorine, you can convert to something else easily. But note It’s really hard to convert from baquacil to anything else.