I think you should tell her immediately...And don't have sex with her pets...

As I understand it, there is a difference between beastiality and zoophilia...
Beastiality is sex with animals...
Zoophilia is being romantically attracted to animals (or a certain one) but understanding that the animal cannot love you back. Usually zoophiliacs don't have sex with animals...
Please correct me if I'm wrong...
While Zoophilia is still a very alternative lifestyle, I don't think it's inherently wrong. (This is my opinion)..
..
I love my dog, and before I found my boyfriend, I wished my dog was human. I would totally date him. He's sweet and loyal, and basically the perfect guy. Except -- he's a dog...
..
Sorry, I veered off track...
..
But still: yes, she should know...
If she loves you, she may not understand, but she won't like, flee...

I think you might be better off being straight with her. It might freak her out, it might not. But at least you'll know for sure. You'd never know maybe she might be willing to try it herself....

I'm a very open minded person so I will be honest in hopefully what I feel is non-offensive. Most people do not condone such practices, and the ones who do would be like you, also zoophiles. I do believe it is VERY VERY VERY important for you to tell her, not doing so would not be fair to her...

Definitely tell her...
..
And seek help...