[Seadog Driftwood]

Several of the ever-popular-with-kids Goosebumps books by R. L. Stine had TF content. In one, there was a dog TF; another had a dog TF and a chipmunk TF, but those two were without process. There was also one with a bee TF, and one involving a lizard TF, I think. I'm sure there were more, but those are the ones I remember.

Sadly, most of those were with male protagonists, but there was another book by another author "Little Pet Shop of Horrors", where a girl is turned into a dog. Again, it's an instantaneous TF, but the results are pretty neat.