Difference between baseball and softball pitching

I know a girl at my school who’s on the varsity team and she’s pretty much the only girl who pitches. Every time I go watch them she pitches a whole game by herself and doesn’t seem fatigued at all. This surprised me, because in baseball a team can’t have one guy who does all the pitching for every time since it causes stress on their arm. Do softball pitchers get sore arms, torn rotator cuffs, or a elbow injury like Tommy John? This may seem like a stupid question but just curious.

My understanding is that the underhand throws don’t cause stress that overhand causes. Don’t think there are limits in softball or that it’s known to cause injury.

I do tend to see a lot of honkin’ sized knee braces on softball pitchers. I see HS softball games and pitchers seem to throw until they get shelled and rarely do they come out for pitch counts. I have not really analyzed it in depth…just general thoughts from basic observation really.