Set goals not ultimatums. They guys above listed the keys to speed. We play first year 14U A ball in Texas. We typically don't see many kids throwing 45 mph. The ones that we do see give us fits one time through the line up and then we typically hit them hard. If your DD wants to continue pitching work on fixing the flaws and her speed will increase. My DD throws mid 50's consistently and can change speeds and levels. and we still to this day work on velocity 3 days a week. It really comes down to are you and DD comfortable with her on the mound from a safety perspective, and are your long term goals aligned in regards to pitching. Its a marathon not a sprint.