Hi,
I'm really sorry to hear that your daughter is suffering so much with her knees. I had a high tibial osteotomy almost 2 years ago, and while it has helped a lot, my knee will never be 100%. I spent 4 nights in hospital and had 4 weeks off work. It was a struggle when I went back to work (office job) and honestly I could have done with another 1-2 weeks off. I don't think I was allowed to walk for 6-8 weeks, so by the time I was allowed to put weight through my leg, my quad/hamstrings/calf had all vanished. I had to relearn simple things like how to walk (that was pretty sad) and had to practise standing up/sitting down in a chair for weeks before I could do it properly.
You have to put a LOT of time and effort into your rehab if you want things to go back to normal (ish). Especially as your daughter is only 15. I had my HTO when I was 28 so still have a long way to go before knee replacements are an option. Be prepared for plenty of pain, plenty of rehab (over a year of working on rehab). You will both need to be very patient and diligent. I didn't realise how major the surgery was before I had it done, so make sure you both understand how much work it will be. Your daughter will need a lot of help, so hopefully there will be someone that can stay with her in the day time to help her as she needs.
If you have any questions please feel free to ask, I'm more than happy to talk about my experiences. Don't let my post scare you off, you just need to know that this surgery requires a LOT of work to get back to where you want to be afterwards.