Hi Kim,
I don't have Crohns, but I have Interstitial Cystitis, a bladder autoimmune condition.. for years, I've struggled with horrible periods. Cramps that would make me miss school, migraines since age 13 that I finally got diagnosed LAST YEAR as cluster migraines (the most severe migraine you can get) and I'm on Topamax for, after 15 years of misery, severe diarrhea... And, many "normal" women experience diarrhea in the days leading up to and during their periods, just google "period & diarrhea" and you'll see what I mean! I have ever since I started. So if even normal girls get GI issues from their period, I can only imagine what it does to someone with IBD.
I as well as many others w IC, and other autoimmune issues (lots of ppl w IC also have other coexisting autoimmune diseases) experience worsening symptoms around their periods. The combination of regular menstrual BS - I'm sorry, but it is total BS lol - plus worsening disease symptoms is really no fun.
Heating pads are def my friend, as well as peppermint tea and hot baths. Also, finally going on birth control at age 22 helped a lot with the cramps & severity of the period itself. My parents were very against birth control, and I suffered for it until I was an adult. Have you discussed bc w her doctor, to give her some relief?