@OmegaFenrir
I'm guessing it's because it's so high level and the fact that it's a slime. Video game logic usually means that slimes are weak and are easy prey for starter players so normally no one would have them as a pet. Hope that helps!
P.S. I don't know what first transfer is. Maybe it has something to do with the fact that she has 2 pets so she has to transfer one pet to her inventory to use the other? It could also just be a ranking system (ex. 3rd transfer, 2nd transfer, ect.)