It's definitely time for a new bat.
My DD (12yo, 5'-4", 120+lbs) is currently swinging a 33/23 Demarini CF8. She's pretty strong, and hits for good power. She has recently transitioned from a 32/32 Miken Freak Black, which she still uses when she feel like she needs a little bit of extra quickness.
The "right" bat is largely about personal preference. For your DD, I would guess that a 32/21, 32/22 or 33/23 might be the "right" one.
Edited for Eric F.