Hi...and I love your user name....lol.
I never did the vegetarian scene as an emergency visit to the ER catapulted me straight from the Standard American Diet scene into the whole food plant-based vegan lifestyle overnight.
I'm not personally familiar with the UC symptoms and such, but had previously been diagnosed with severe Irritable Bowel Syndrome, nervous stomach, acid reflux, morbid obesity, and multiple other issues not directly digestive related.
I gave up all meat, dairy, eggs, caffeine, and alcohol and, other than some rough patches from the initial drastic shift and the learning curves, most of my digestive suffering ended, along with several other things I'd been told to "just get used to" as a natural part of aging and/or genetics. I then discovered genes aren't the only things that run in families, so do diets. lol
I'm curious if you've tried eliminating dairy and eggs for any length of time to see if that has any additional helpful effects. If so, my apologies for going where you've already been.
"Strange times are these in which we live when old and young are taught falsehoods in school. And the person that dares to tell the truth is called at once a lunatic and a fool." ~Plato