NOT A TEACHER
There is no particular reason why he said "gal". "Gal" is just another (informal) word that means "woman" or "girl". It's commonly used in AmE.
I don't know exactly what he means by "has got teeth", but I assume that he's praising this author by saying that she writes very suspenseful books. In any case, "has got teeth" is saying something positive about the way the author writes romantic suspense.