"Prey" means an animal that is hunted or is being hunted. But it has a different meaning within the phrasal verb "fall prey (to)." Sometimes you can't get the meaning of a phrasal verb by using the definitions of the individual words. Both Joy's and Alex's explanations are good ones.

"fall prey" could be replaced with "be a victim" hope that helps

It means she will not fall for the deceptions, as in she won’t believe in them because she knows they are lies

Victim