I have a close family member with it.
We use Ph drops (I get them on Amazon) to add to water (and we buy alkaline water to begin with) to give them a head start on alkalinzing their system. When the IC was really bad, daily doses of baking soda really really helped (especially at night). We add the alkaline drops to acid-free coffee (decaf acid free is really pretty good - so iced coffees and BPC is still a possibility).
Because I cook for someone with IC as well as being keto, I pretty much know the drill. All the acid foods are eliminated (lemon, lime, chile, vinegar, etc). It's kind of a drag. But you know what? That Cystoprotek stuff REALLY works - they say it takes six months, and after six months, the situation here is greatly greatly improved (um, I'm going to say "stable" and we had something with a little lemon on it last night - and it was pretty amazing to have that flavor back; can now use a little vinegar here and there too).
Buy dye-free benadryl to help control the production of mast cells in the bladder - use liberally at first (like every night). Be careful to use non-acidic pain killers (tylenol is okay, IIRC).
There's a subreddit that's really helpful:
The sufferer in our household lives off of chicken, steak, salmon, tuna, and salami, mortadella and cheese. I know sometimes these things are said to be triggers, but not in our case - the alkaline water on the side, I think, is really helpful. We do try to get ones without excessive nitrates. Lots of eggs. Beurre blanc, butter, heavy cream (fats are soothing).
Good luck - you can do keto with IC - but do look into Cystoprotek. It's expensive, we were skeptical but a dose is never missed (3X a day and never forgets to take it - you can get the ingredients separately, but the people who formulated are two urologists who really know what they're doing in rebuilding that damaged cell layer in the bladder).