Well, the first question is - do you trust your coach? If you do, then, I would go with that. I would also ask the coach for his/her feedback on why the jumps are a struggle. Is it a training or attitude or whatever issue? And, if your daughter is discouraged, sounds like time for the coach to do some coaching on that front as well as on the skating front; coaches generally do want to know if there is an unhappiness factor with a skater.
Otherwise:
Age 13 - sounds like puberty - are there height or dimension changes? if so, then perfectly normal to lose the jumps; also if the coach is improving the jumps, then, losing them is again normal before they are returned "better". Out of curiosity: have the spins also been inconsistent? These are also often affected by puberty.
Yes, you certainly can maintain those jumps on that amount of ice, particularly if she works hard and isn't also spending huge amounts of time on other disciplines (dance, MITF, etc). She can also do off-ice to strengthen and train the jumps - coach should be able to direct you there.
Skaters gain and lose jumps regularly ... but, it's hard when it's happening to your kid to maintain that perspective.