As the earlier responses made clear, starting at 8 is fine. However, I think it will be tough to spend a substantial time learning pitching if for three years she doesn't get the chance to put it in practice. Most kids get interested in pitching when they see others in their league do it. Aren't there any leagues with live pitching? ASA leagues normally start live pitching at 7 (possibly without walks).
I agree with EP Dad that it would be good to start with a proper instructor; I know that trying to do it myself I did almost everything wrong. On the other hand, an instructor may expect more of a continuous commitment than an 8yo is willing to make. At that age, my DD was willing to practice pitching during the season, but once the season or all-stars was over, she needed a break (she only started lessons when she was 11). I've seen some kids who killed at 8, due to their intensive practice schedule, but were burned out and quit softball altogether by 12.
I agree with EP Dad that it would be good to start with a proper instructor; I know that trying to do it myself I did almost everything wrong. On the other hand, an instructor may expect more of a continuous commitment than an 8yo is willing to make. At that age, my DD was willing to practice pitching during the season, but once the season or all-stars was over, she needed a break (she only started lessons when she was 11). I've seen some kids who killed at 8, due to their intensive practice schedule, but were burned out and quit softball altogether by 12.