The weight of the bat will be determined by the player's strength. Generally at that age and bat length you are looking for anything in the range of an 18oz - 20oz bat.
We would recommend a 32" or 33" length for her height and weight. Both of these bats are excellent models and have been top sellers for us in the fastpitch category, so I don't think you could go wrong with either model.
Based on your player's height and weight, I would recommend purchasing a bat that is 31" in length.
Unfortunately, we are sold out of the 31" size in this 2017 DeMarini CF9 Fastpitch Softball Bat (WTDXCFP) and we will not be getting that size back in stock. The 2018 version of this bat, the 2018 DeMarini CFX -10 Fastpitch Softball Bat (WTDXCFP), will be available in the 31" length.