The difference in a -9 to a -11 will be two ounces in weight. For example, the 32 inch bat you discussed will weigh 23 ounces if you chose a -9. In comparison, the 32 inch bat with a -11 will weigh 21 ounces. In my opinion, I think the 2018 DeMarini CFX -9 Fastpitch Softball Bat: WTDXCFF will be too heavy for your player. I would recommend the 2018 DeMarini CFX -11 Fastpitch Softball Bat: WTDXCFS if your player needs a lighter bat to help increase her bat speed.
Based on your player's height and weight, I would recommend the 2018 DeMarini CFX -9 Fastpitch Softball Bat (WTDXCFF) in the 34"/25 oz. size.
If you were comparing similar length models of this 2018 DeMarini CFX -9 Fastpitch Softball Bat (WTDXCFF) and the 2018 DeMarini CFX Insane -10 Fastpitch Softball Bat (WTDXCFI), this bat will technically be the heavier bat (due to its -9 length-to-weight ratio). However, the CFX Insane will have extra weight displaced into the barrel of the bat which will allow some players to possibly use that bat and put a little extra force into the softball and hit it further. However, if a player is looking for "heavy" feeling bat, this CFX (-9) or the CFX Insane (-10) should suffice.