Faustina might work. It could easily be shortened to
Tina. I think "
Faust" is a rather obscure work by now: I've never heard of it until I found this website. After all, Spanish people freely use
Fausto and nobody complains about it.
I slightly prefer
Faustine, though.
Fauna wouldn't work as well IMO. After all, it's the scientific term for animals, especially in a given area. Though
Flora is the same for plants, and no one has a problem with that, so maybe
Fauna could work. Just don't name two daughters
Flora and
Fauna - that is EXTREMELY tacky.