OK, how about checking her out thoroughly before any more a/bs? Get someone to hold her steady and, using both hands on both legs, start from the top and close your eyes! This will allow you to really concentrate on what you're feeling. Feel down the leg, gently and slowly, working around the joints and bones. Feeling the good leg at the same time as the limping one gives you a reference point for swelling, heat and so on.
If there's nothing obvious put some warm water in an old basin and keep the foot in it for a few minutes, until any mud can easily be wiped away with a bit of old duster or similar. Resoak the foot if necessary. Now have a look, particularly between the clees. Is there any pinkness (use a good foot for reference), any mud or a stone or piece of straw stuck under the edge of the horn? Feel around the top of the horn too, where the hair on the legs covers it. The hair may be hiding a small thorn or abscess.
If she recovered and is now limping again it's most likely something completely new.