I would say you really need to have a second AND a third opinion.
I got three, and the third was from a gastro who usually wants to give meds and not operate, and she said I should have the surgery within a few weeks. I didn't just have uc, but also had a long nasty stricture in the colon that would probably have closed in completely within some months.
But you definitely owe yourself 3 opinions. Behm should respect that and refer you to equally ranking colleagues.
There two kinds of doctors - the kind that want to use surgery as absolute last resort and give the patients nuclear warfare medication. Then there is the other kind that sees surgery as a way to prevent all kinds of nasty things from happening, and also to spare the patient further flares (that are getting worse) despite intensifying the drug therapy.
Your attitude about the surgery is really great, it's great that you are keeping the big picture in front of you. People in their 20's heal really fast. Living with the stoma and the bag is quite a trip mentally and emotionally, but only in the beginning, and it's only for a few months anyway. Afterwards, you'll be there for your daughter much more than you can now.