Seems like that’s just something to clarify with the camp hosts the next chance you get. It’s probably not anything nefarious, just an attempt to preserve the wilderness experience.
Maybe they’d make an exception given the medical considerations here.
The power consumption would be minimal. A phone with a minimally healthy battery could handle three days of that. Also, I’d like to think that at least one of the adults brought along a battery pack or power pack for just in case (unless this is like some really well-traveled camping/hiking area).
InReach is great, but it’s not for one-off use. It’s like a $300 device with a $12/month subscription (in the US). You can also get a plan that turns on and off, but it still has added fees. I’ve figured that if I have use for it 3-4 months in a given year, it’s cheaper to keep it on.
There are also “personal locator beacons” which don’t allow communication, but do provide an “oh shit” button.
I keep airplane mode on all the time, if I need to try to use it on a mountaintop I’ll turn off and check for a signal. It’s amazing how many orders of magnitude shorter battery life is if constantly searching for a signal. Not getting signal updates for 10 or so hours is normal, I wouldn’t specifically worry, OP.
Oh phew, the Duke of York outings for young women are the ones you really want to worry about…
Heh heh
Never mind
Not to get preachy about this, but I’d be surprised if being harder to reach wasn’t a deliberate choice. It’s a philosophical thing, just a common part of the outdoor ethos.
I think part of the allure of escaping to the woods is getting to deliberately disconnect from the world for a few days. Having to check your phone every few hours takes away from that experience. It’s one thing to have a satellite messenger in case of emergency, but having to turn off airplane mode every hour, scan for a signal, look at your notifications, swipe away all the irrelevant ones, answer every parent’s check-in request, try to figure out who the missed calls are, post a group selfie… that would really take away from the experience, I think. Even if you were in camp the whole day, the passage of time would feel completely different, and more artificial than a day in the woods would normally be.
I can’t speak to the OP’s medical situation with their wife (hope it’s OK!), but in every outdoor group I’ve been a part of, being out of reception for a few days was a completely normal, expected thing. Everyone has family and friends and something could happen to any of them while you’re out of range, and that would undoubtedly suck, but that’s understood to be an acceptable risk of the experience. Maybe part of the allure. It’s very rare we get to focus on the world around us instead of something online.
Anyway, it’s not a right or wrong thing, just something to be discussed with the group participants beforehand so everyone’s on the same page.
I’ll agree that the school maybe should have been more clear about how reachable the team will be while they are gone. Then you could have made the decision to keep your daughter at home.
But regarding running down the battery? I’ve taken train trips from Chur to Andermatt and forgotten to put my phone in airplane mode and was amazed how quickly my battery got drained. And those trains don’t have outlets. 
Most Swiss mountains do have good network coverage, but it is not 100%.
The Airtags, assuming they are paired, should tell you when the battery needs replacing.
Typical Swiss behavior. 
At least she has good weather, if she’s in the Western pre-Alps.
Yes, it’s really nice this weekend. Our narcissuses and crocuses are in full bloom.