I played three sports through the end of high school and 1.5 in college (varsity football plus moonlighting in some open wrestling tournaments for fun). The only "off" season where I could just work out was the summer. Nine months were spent figuring out when to lift/run around my practice schedule. It can be done. Just don't try to teach too many new things all at once. She's 13. Most girls her age are probably doing very little outside of practice to prepare for games, so your daughter will be ahead of the curve just by virtue of doing ANY extra work. She doesn't need a "program" that hits everything. She just needs a good grounding in the basics of strength.
Practices will handle most of her conditioning, I take it. So my guess, without seeing her exact practice schedule, is that you'll get the best bang for your buck with a few well-placed strength workouts. I think that teaching her good squat and clean form is a good idea, and kettlebells & med-balls are nice for warm-ups and finishing work.
How frequently can you actually supervise her workouts (and more importantly, what is her attitude towards it - does she like working out, or tolerate it as a necessary evil when she'd rather be at sports practice?)
Is your intent to be there for all of her workouts, or just to teach her good form so she does it right when her team has a lifting session? FWIW, my dad taught me to lift when I was a pre-teen and, although we did not lift together more than once a week during the school year (he lifted at nights after work, I usually did so during school or as part of wrestling/track practice), I kept those good habits.
If she's practicing 4-5 days a week plus games and camps, that's going to take a lot of energy on its own. So don't browbeat her with advice that she's tired of hearing. Find a couple of things she likes and drill them well. It could be 10 minutes of warming up with a KB, a few good sets of squats and cleans, some med-ball slams, and you're done. That'll benefit any athlete.