I would recommend getting a fastpitch softball bat in the 30" length. This 2016 Louisville Slugger XENO Plus Fastpitch Softball Bat (FPXN160) has been an excellent bat for a number of years. It will have your two-piece, all-composite design and a balanced swing weight. The LXT will feature the same material, but it also features an advanced connection point that allows for more barrel flex at contact and limits the vibration that gets to a player's hands on a miss-hit. If you want the model that technically has the most technology, I would suggest an LXT. However, the XENO can be bought for slightly less money and I think it has the potential to perform as well as the LXT.
Based on your daughter's height and weight, we would recommend getting the 2016 Louisville Slugger XENO Plus Fastpitch Softball Bat: FPXN160 in a 33/23.
I would suggest the 2016 Louisville Slugger XENO Plus Fastpitch Softball Bat: FPXN160 in a 31" 21oz. size based on her height and weight and the fact that she is used to the feel of the XENO.