If this has been talked about to death, forgive me!

I've had my beep for about 2 months and she's settled in well. (she's about 3 months old).

I've noticed a couple threads talking about the beeps needing some stretch room. Is there an average size / age that you'd want to move them into a bigger set up? I also ask since Coco is now taking Rat fuzzies and she is sitting up more to get the bigger prey items down, and I felt bad as she was a bit close to the top of her tub as she was swallowing the last of the rat. Am I worrying too much, too early?

I have a tub size up and an exo-terra front opening tank I got gently used from a friend to move her into as she grows.

Thanks everyone!