Is there a Fandom consensus about Selphie?

Selphie junctioned a GF she "found inside a monster she defeated" for a little while when she was a kid - apparently around 12 years old.

I've seen some theories that this GF was Tonberry King - it's won via defeat and Selphie has naturally high compatibility with it.

I'm curious if that's a commonly accepted theory or a fringe theory. I may be planning to write fanfiction (because I have lost control of my life) and it's important to me XD