Yes IBD does flare and what controls it varies from kitty to kitty. Diet changes help some kitties other kitties need a low maintenance type dose of steroid. My kitty is on a low dose of steroid and has done well for 4 years now but he has started losing weight. He has no other symptoms but the vet is doing another ultrasound on March 3 to see what is going on with him. http://www.ibdkitties.net/ has a lot of good info. You can also type in IBD on the search bar at the top of the forum here and it will bring up a lot of threads, many with lots of good info.
My old boy had IBD, and what started us down the road in figuring that out was that he had a pancreatitis attack. He had those sort of flare ups twice. Really the only thing our vet did was recommend supportive care during that time. My old boy never got diarrhea but he did throw up alot! So the vet gave him anti-nausea (cerenia) and an appetite stimulant and sub-q fluids. My boy took about a week or two to fully recover.
I hope your kitty gets better soon, I know how stressful and emotional it can be!