One thing to check if your horse is lame, is the digital pulse.
Find the digital arteries, which are on the inside and outside of each leg at the level of the fetlock and pastern. (ask your vet to help next time she's out)
If the pulse is throbbing, laminitis is a big worry! My vet is of the opinion that the pulse will often rise a few days before founder occurs, so there might be time to prevent it.