My understanding this is the biggest indicator of bad bat drag. They hit the snot out of the ball when facing younger slower pitching but when they get older and face better pitching they start to struggle. Good thing is you recognize there is a problem and are looking for fixes. Most parents never realize their is a problem and think their daughter is fabulous everytime she really cranks one, problem is that don't/won't happen often. My suggestion would be to search and read everything Hitter has to say on here. There are others on here that are very knowledgable but I took my daughter to one of Hitters camps with Bustos and what they teach works.
No doubt Hitter has methods to deal with the problem.