I'd get a stool test for possible infectious causes, things like c diff. We all flare eventually, even on the strongest medications like remicade, and we will bounce back with proper treatment.
You can ask her doctor about
a test like this: https://www.labcorp.com/test-menu/29496/infliximab-concentration-and-anti-infliximab-antibody
which checks for remicade-antibodies, and checks the levels of her medication just prior to the next infusion. It helps answer if she's running out of remicade too fast, has antibodies and the medication is becoming less effective, etc. Simply increasing the frequency and/or dosing of remicade can usually bring her back into response.
Moderator Ulcerative Colitis
John, 40, UC Proctosigmoiditis
Rx: Remicade @5mgs/kg/6wks; daily 75mgs 6MP, 4.8g generic-Lialda, and rowasaYou never really appreciate what you've got until it's gone. Toilet paper is a good example.