Well it looks great now! Mine was done for the same reason. I forget the degree it was at the time of surgery, and despite wearing a brace from when I was age 6-12.5 (they let me have 6 months of no brace before the surgery) the curve was very severe and there was no option other than surgery.
As I said I was in the hospital 10 days, a body cast for 7 of those and then the lovely Milwaukee brace 24/7 for 10 months. I believe they spare kids the brace afterwards now?
Actually I kid about it being horrible, it really wasn't. Even though I was in junior high nobody teased me or harassed me or anything. Everyone in my grade pretty much knew I wore the Boston brace prior, so even though the Milwaukee brace was actually visible it wasn't a huge deal. And it got me out of PE for a year, so silver lining.
As an adult now, almost 40 years post surgery it is hardly on my radar. My back feels great (I know that is a concern my parents had), I am obviously not very flexible with 2 metal rods in my spine, but my posture is good, no slouching around here.
The time of my surgery is nothing but a blur to me, the main thing I remember from my time in the hospital is my friends coming to see me, my cousin hanging up posters from Wham! in my room for me to look at and the tilt table from PT. I don't harbor any memories of the pain, being sick from the meds or anything. I think your mind erases that for you. I doubt Finley will remember it either, at least I hope so.
That year after surgery there wasn't anything brace wise that was too memorable either. Except my best friend not realizing I got my brace off. I didn't tell anyone because I hadn't known they were going to be taking it off at my doctor's appointment. I thought it was just my normal monthly check up. The next morning when I went to school and I didn't have my brace on I was hanging out my best friend before school - we were together for like an hour working on homework in the library. She never noticed. Suddenly another friend of ours came in and yelled "hey you got your brace off!" my best friend just looked at me and was stunned. She become so used to seeing me in it she didn't even notice it anymore.
I know this was long and kind of rambly but I know my mom had said she wished she had been able to meet somebody older that had had the surgery and know that everything was going to be fine. She had been a Hospice nurse and she had seen what happened when people didn't have the surgery but not anyone who had. She told me many years later she was always worried it would impact my quality of life somehow and it really hasn't.
I know there are a lot of negative horrible things you are witnessing as a parent. It is horrible to see your child suffering in pain and worrying about them but honestly I don't think Finley will remember the hospital stay and if she does it's going to be a blip in her radar pretty soon. She will have other things that squash out any negative memories. I wish you all lots of love and luck and peace!
Oh, one thing I was concerned about as a child was would I be able to ride rides. I love roller coasters but they have all those warning signs about not riding if you have a back injury. I can positively say I can ride anything and everything with no back problems at all. Even the Matterhorn. Not sure if anyone in your family was worried about that, but since I had just been to DL for the first time prior to my surgery that was my 13 year old self's primary concern
But all good here, in fact I am the only one in my family who will ride everything at DL or WDW except the Scaris Wheel at California Adventure, but that is not a back thing, that is purely my brain telling me that ride is terrifying.
I doubt I can be any help but if you do have any questions or anything let me know I'm happy to try to answer and offer any insight that you might want.