So sorry to hear your daughter is having a problem. Blood can be caused by several things and she needs to see her GI or surgeon. I've experienced the same thing and it ended up being cuffitis.
Cuffitis can occur where the j-pouch is attached, double stapled usually, to the rectal cuff. If like my case, the surgeon left 2 cm of my rectum attached to the sphincter muscle and the j-pouch was stapled to that 2 cm.
I don't know about your daughter's surgery, she could have had a different kind of attaching. If she had surgery like I did, that 2 cm of rectum left to attach the j-pouch can still get UC. They call it cuffitis but it is UC. You would think it's not enough to cause a problem but it can.
It is a problem that the doctor can check out without doing a scope. The rectal cuff isn't to far in and it can be digitally checked to see if it is inflamed.
I have taken 2 different kinds of suppositories to get it in check. Canesa worked the best for me. Another one they use is Anucort.
I hope it's just a broken blood vessel or something like that causing the problem but suggest she get it checked sooner than later.
They told us we would be cured after the operation but in my case they were wrong.