Hey there!
I understand the anxiety so will share my experience.
I had corrective surgery aged 21 (ten years ago). It does seem that you're considered positively jurassic by that age, in the scoliosis world! My largest curve was 86 degrees. It got so out of hand due to various phobias but eventually the pain was too unbearable so I sought help. My only regret was leaving it so long.
I have quite an extensive medical history so had to seek a second opinion as the first surgeon I saw felt that the risks were too great in my particular situation. After pleading my case, the second surgeon agreed to operate.
I'd built it up in my head for so many years that honestly, the whole experience was a breeze in comparison to what I had imagined. After the first surgery, I actually felt no different, like nothing had happened. The second stage was a little more tough. The worst bit for me was the feeling of unfamiliarity. After so many years of my back muscles and spine being in that curved and twisted position, to suddenly have everything moved into a new position was very odd and uncomfortable for a bit. The other thing that I didn't like was the chest drain but that was removed quite quickly I think. The first 48 hrs were rather a blur due to the morphine!
They don't hang about with getting you back to normal. It's quite amazing really, just how quickly this process starts.
I personally think a lot of the recovery experience is down to yourself, as a person. For example, I'm no stranger to being in hospital and experiencing pain due to my other health problems. If your DD is otherwise healthy she may find it more challenging than I did or more painful if she isn't used to pain. Does she want the surgery? I really wanted the surgery, which also helped I think.
Having a surgeon who you trust is important. Don't be afraid to ask for a second opinion or to see someone else if that's what you feel.
The upside of being a 21 year old scoliosis dinosaur was that I was in complete control. I got to ask the questions and make the decisions. Had I been 14 it would have been more of a family thing where no doubt I'd have been angry at all concerned and very bitter during recovery.
It is a scary thing, whichever way you look at it. Being informed, asking lots of questions and knowing what to expect at each stage definitely helps though.
Best wishes for you and your DD :)