I had this done when I was 12 - I'm afraid I cannot deny it was the most painful thing I had ever experienced (until I gave birth). I did have a local anaesthetic, so the actual procedure wasn't too bad, but it wore off pretty quickly, and the next 24 hours were miserable. I lay in bed crying for a long time and couldn't touch/blow my nose for several days.
But, IT WORKED!! and the miserable hours of nosebleeds I used to suffer became a thing of the past.
This was a good few years ago, so I imagine things have improved, but it is a sensitive part of your body being cauterised, so some discomfort is probably unavoidable.
But I would definitely go for it. Chronic nosebleeds are utterly miserable. Good luck to your DD, hope she gets through it OK.
My DS had this done about 8 years ago, just done with a stick thing (very technical!) He was fine, but it was a bit sore. He had the cream too, which helped. He was having very spectacular spontaneous nosebleeds 3/4 times a week, caused by enlarged blood vessels. It definitely helped, but didn't stop them completely.