How far off farrowing is she? I'd be inclined to keep her out of the mud. She'll use a lot of energy just walking around in it at the moment and she has better things to do with her calories, like grow her piglets. I once sold a top quality young, pedigree, in-pig GOS sow to a fairly new keeper and after weaning she was kept outside in muddy conditions all through a cold Winter and developed arthritis.