For my dd (18U - not growing anymore), developing her glutes and doing strength training that improved her core and balanced out her upper body strength truly helped this past winter. We found a really great trainer who works with mostly baseball players but he did some research and developed a very specific program for her.
^^^ this^^^
My DD
10 year old 50 mph
11 yo 50 mph
12 yo 51 mph
13 yo 52 mph
14 yo 54 mph
15 yo 55 mph
16 yo 56 mph
17 yo 60 mph
18 yo 63 mph
Found a great ex-MLB trainer who mitigated her quad dominance through a year of building up her backside (glutes, hamstrings) and core strength.
Also, don’t forget about stretching.