Many slower kids have poor hip flexor strength and struggle to lift their knees high when they run. High knees leads to a longer more powerful stride.
You don't need any special equipment or complex drills to improve on this issue.
Try the 100 up drill to increase strength and flexibility...
My DD's glove is actually a 12.5". I said it was 12" in the earlier post.
Bought our A950 at Dick's and let them steam it. I also baked it at home with Barbasol. Still stiff enough where she has to use 2 hands to help close the glove on fly balls (not a bad thing!).
Since she's a little...
Picked up a 12" Wilson A950 in the spring for my slightly below average sized 12U. She played primarily CF and SS, with some LF and 2B.
https://m.dickssportinggoods.com/p/wilson-12-a950-series-fastpitch-glove-2018-17wilw12950fpbrwnfpg/17wilw12950fpbrwnfpg
With coupons it was under $70.
She...
Glad it's working out.
My DD was the same way a year ago. I wasn't as nice as you however. I signed her up and made her go and she's having a great season. I prefer to push my kids into doing things that are a little uncomfortable for them.
My DD is 11 (almost 12) and slightly below average in size(4'8" ~75 lbs). She got the Stealth Flex 2017 30/19 and is killing it. We got it for a similar price.
Sorry to hear of your latest injury. That really sucks. Fortunately, my DD has only suffered from scrapes and bruises so far.
Some of your injuries are accidents and can't be helped. Others are recurring issues - back spasms, tendonitis, knee and ankle issues.
When you are mended, perhaps get...
Bat on shoulder - Does your DD DBSF?
If your daughter (or you) doesn't understand what the instructor is trying to accomplish, then tell the instructor you don't understand. A good instructor will have different ways of teaching the same thing. What works for one person will not necessarily...
Talk to as many other parents as you can about instructors. When I coached I would ask other coaches who they recommended. Now, I seek out good players & their parents on the other teams after games.