I would *never8 use Petunia as a name, not even for an animal!
I've never known of anybody human named this either.
First of all, I don't like the petunia flower. It doesn't smell good and it makes my nose swell and itch if I get too near it.
Also, there's Petunia Pig, Porky's girlfriend or whatever she was. And Harry Potter's nasty aunt Petunia Dursley. Just a bunch of bad associations.