I think it depends on how severe the case is.
Walking them definitely helps. But if they're not passing anything, I'd be worried. There may be an impaction of some kind. Sometimes it may take surgery. Meanwhile, keep her moving. They usually don't want to, but they should.
I've heard of horses colicking for several days. Usually the owner doesn't have a lot of exposure to their horse, or doesn't check on them everyday, and it will go unnoticed. A bit of bad behavior over a period of days starts to add up when the horse starts to kick his/her stomach violently.
I have a mare that, I believe, had a weak case of gas colic for a few weeks. Then one day it just got really bad, and I finally noticed. I didn't realize she was in any pain before that point; she was really stoic. And I interacted with her for several hours a day at least. Found out that the pasture she was on (she was boarded at a stable) was about 75% fresh alfalfa. It was way too rich. Most of the horses there had diarrhea constantly or colicked at least once a month.
It sounds like you're doing the right thing though- walking her.