I'm going to tell my friend she is a cat whisperer
What is your reason for thinking that your friend is a cat whisperer?
She knows tons about cats and has very deep conversations when she talks to them.
It sounds like you're a good friend! Being able to connect with cats can be tricky and complimenting your friend on her unique talent is a very thoughtful thing to do.
I'm going to lie to her that I like cats just so I can try to describe how my imaginary cat sounds like when it was at the vet, then I'll ask her to tell me about all the problems my cat had.
It is really cool of you to compliment your friend based on her talent. Her talent sounds very unique, and it is cool that you are giving her a label for this uniqueness. Try your best not to lie to her though, as honesty is very important in any relationship.