B.C.
Did you take her to the doctor when this first happened?
Having her thumb locked in one position for a year would have me worrying about her growth and development of her hand.
Muscles locked in one position may atrophy over time.
Read up about what this condition is.
http://orthoinfo.aaos.org/topic.cfm?topic=a00024
http://www.healthline.com/health/trigger-finger#RiskFactors3
http://parents.berkeley.edu/advice/health/triggerfinger.html
If it were my child, I'd have the surgery performed and I wouldn't have waited a year to have it done.
Any physical therapy that's needed to help her recover - do it.
She needs the use of her hand/thumb her whole life.
Additional:
Thanks for the additional info!
It sounds like you've been on top of the situation but your doctor didn't inform you of a splinting treatment option.
That would tend to make me think I need to get a new doctor.
If he didn't inform you of your treatment options I've got to wonder what else he's not covering.
This sort of surgery is easy peasey.
I had a few benign cysts removed from my left hand on two different occasions when I was a kid.
Back in the day (this was the 70's) they kept you over night in the hospital for everything.
Now they turn things around and try not to keep anyone over night unless it's something major and heck - even open heart surgery patients are home in less than a week.
Surgery is sometimes necessary and you do what you have to do for the sake of your kids - even swallow your fears so they don't freak out.
I know a guy whose 2 yr old had open hearty surgery to repair a hole in her heart - everyone's fine and living happily ever after.
Take her to a pediatric orthopedist and see what he has to say.