Foot rot is only one of many causes of lameness. Your description makes me think the cow has a systemic illness (disease of the whole body) rather than a localized (one site of the body) infection like foot rot. Many infections make the animal feel bad and have aching joints. (Think about the last time you had the "flu.") For example, these might be signs you would see in a cow with hardware disease or other infection in the abdomen. Sometimes cows in late pregnancy walk stiffly because a large calf is putting pressure on the nerves. These cows often recover after calving.
You may need to have a veterinarian examine the cow to find out what is going on or how to treat her.
