She shouldn't lose them; in fact, it might be a good thing to take a break. Muscle memory kicks in when you're off the ice for a period of time. Based on the directions of Skate Canada for periodization, skaters should take at least 2 weeks off between seasons to rest, heal and re-energize.
Working from the experience of my own kids (and many others, I'm one of those analytical types and I hang around rinks a lot): coming back from an extended break, they are stronger and more focussed and have not lost anything. It takes about 2 days to get back in the swing of things. They are also refreshed and ready to attack; and we see huge gains in the weeks after the return. In this past month alone,since back from our spring to summer break, we have gained a more consistent double axel and two triples for one kid; an axel, a 2S, a 2L and a 2F for another; and, a proper spiral, back inside edges and backward crosscuts for our tiniest. Other skaters in our club have similarly progressed, however, the ones who didn't take a break seem to be struggling and plateauing ... and are tired and not nearly as enthusiastic. I've chatted with coaches about this, and apparently, they see this as a pattern as well, and encourage their skaters to take solid breaks.
In terms of doing off-ice training: do some cross-training, build up cardio and endurance, work on core and upper body. Get uber-healthy. dMost importantly, have some fun ... skating is hard work, and kids need to have fun or they burnout. Do the stuff that you normally don't have time for. If there is some type of "thing" that you can't do or start normally because you're worried about it messing up skating - for example, my one kid wanted to go back to distance swimming, which would be good, but, would negatively impact her skating during the start-up period as she got back into it, so she did it during her skating break, and is now nicely working the two together.
In terms of doing some - different - types of off-ice training: do visualization. The skater lies flat, eyes closed, and visualizes themselves landing the jumps with good technique. It sounds odd, but, their are multiple studies that validate that visualizationi is an excellent training tool.