Oh dear. I'm so sorry. Is the vet sure it's just colic? While I'm no expert - never had a horse with more than gas colic, and we cleared that up without having to call the vet - it sounds like it might be something a bit different.
If it's just colic, could the vet leave you something for pain to give her until it clears up? That might save you another trip, then again, if it doesn't clear up, he may need to re-assess the situation.
Sending healing vibes your way!