Bat question - stay with the same weight and go up in length?

[Caredeocr]

My 10 y/o daughter has been using a relatively cheap Rawlings bat, 27/15. She hits it ok but I'd like to get her a better bat for the upcoming spring season. Should I stick with the same weight but go up to a 28 (so it would be a drop 13, which I've heard maybe should be stayed away from) or go up to a 28/16 (drop 12)? I was looking at the Demarini Zenith 28/15.

Thanks