What To Do With New Kitten?

I have a new kitten that I am not sure what to do with. We are in the process of getting her fixed, but she is doing great otherwise. She’s eating and drinking well too! I was told by my vet that if we don’t get her fixed, she will run away after puberty (or sooner). My aunt has 3 cats so I knew it wouldn’t be an issue for them to take care of her until then. They kept saying that you shouldn’t get a cat before 6 months old because they can be temperamental or just misbehave when they lose their mother at this age. The problem is she came from the shelter before 6 months old and never had any kind of treatment since then which could lead up to hormone issues later on in life? What should we do? Any advice would help!