If the soft tissue immediately above the hoof is definitely swollen it very likely is foot rot and antibiotics as soon as possible would be nice (though difficult in this situation).

On the other hand, if there is no swelling it may be a sole abscess, which are painful to the cow, but could wait until after she calves.  Often sole abscess will open and drain by themselves.  I often give them antibiotics but they seldom respond well to that....