IsabellaLinton,
Hydroxychloroquine: might help a tiny bit via inhibiting Cathepsin L, so spike processing might be slower
Azathioprine/Prednisolone: will likely hurt a bit, but overall not much; the good news is that kids on immunosuppressants don't seem to be much different compared to those that aren't, which might point to things about the cause of severe disease, and I don't think it's all to do with innate immunity (that's another lecture zone that I'll spare everyone)
I'd cautiously monitor, note time of symptom onset and then watch the progression carefully as the days go on. Symptoms getting worse or new concerning ones as it goes on are what you watch for (it should stay fairly stable throughout the week, just with the usual ups and downs throughout the day, which you likely experienced), along with what most would know, like marked weakness, shortness of breath, really high fever, and/or altered mental status. Pulse oximeter. Her doctor knowing she has it and informing them if there's anything you're worried about. Things like altered mental status, low 02, and/or marked weakness are hospital time. Fluids, rest and all the rest. This is just me, a professional autistic.
I sometimes feel I'm lucky that I'm a broken mess, as I'd worry far too much if I had children. Sorry for you there.