As she's on antibiotics I would chalk it 100% up to that. However, I would say blood in stool is the only indicator I would consider for an UC, as even those without an UC have occasional loose stools, a day with more frequent stools, bad farts, or the occasional accident, and more so with young children.
I get it that nobody ever wants is/her little ones to suffer with an IBD/UC, and with only one parent with an IBD, the odds are fairly low. "One study estimated that the risks of IBD in first degree relatives of probands with UC were 1.6%, values that were even higher in the Jewish population. If both parents have IBD, the risk of their offspring developing IBD over their lifetime was estimated to be 36%."
So, that's saying the absolute risk of your child getting UC is 1.6% and the odds of him/her not getting UC are 98.4% with one parent with an IBD. If both parents have an IBD then the absolute risk is 36%. The odds are greater that that of the general population (multiple times) but are still very, very small in absolute risk.