We had a flamethrower last year in 13u. She was throwing in the low 60's. Unfortunately, she came up from a rec league and she was absolutely enthralled with her speed. She had a curve and a screwball that moved approximately 10" or so. They had great movement but happened to stay on the horizontal plane and were every bit as fast as her FB. Because she was so used to overpowering her opponents, she absolutely refused to work on her change-up and slowing down her CB or SB. Needless to say, when we faced teams that practiced hitting that speed, she got tattooed all over the field. I am a strong believer in developing 3 speeds if not 4. I am also a strong believer in developing the up-down movement as well as the side to side. That being said, IMO, a flamethrower that can throw a drop curve at 60+ mph has a much better chance of success in the K department than a pitcher that can pinpoint her FB. I'm not saying that the occasional FB isn't warrented, just that it is a much easier pitch to hit on a relatively flat plane than some other pitch that is changing planes up or down;especially when hung over the plate by mistake.
Thats remarkable that a 13yo throwing 60+ with 10" (two and half balls) of lateral movement would get tattooed all the field.
While I agree about the need to change speeds, 10 or so inches of movement at that speed should move the ball off the sweet spot often.
My DD is a Soph at D3 this year, tops out at 62 and has about three balls of movement laterally.
I'm glad she doesn't face your 13u hitters.