First, don't give her some random, old antacid you got at an auction. Throw that away immediately
. I can't believe you'd even keep it, much less think about giving it to your horse.
Second, give her as much water as she'll drink. Dehydration can cause impaction colic, so taking water away from her can bring on the very colic you're trying to avoid.
Third, she may not colic but she could
founder from overeating. Making her exercise on top of the overeating could have jump started founder.
Fourth, it wouldn't hurt to give your vet a call and get an examination done on your mare.
Keep an eye on her for the next 24-48 hours, and check her feet periodically to make sure they're not hot. Hot feet are one of the signs of founder.
It's not only colic you have to worry about when a horse gets into a feed bin and gorges itself. Colic may be the least
of your worries.