Hiya Helen,
Only just caught this thread, I agree with Mandy, treat her asap ! Anti-biotics and udder cream (if she'll let you) I've seen stuff which is minty, so it cools the udder too - it will be hot and uncomfortable for her. Teats tend to get red, a bit lumpy and uneven when rearing a litter anyway (just think of breast feeding in humans) but mastitus is a different thing and should be treated straight away. I wouldn't advise early weaning (sorry to be contraversial) keeping the piglets there, suckling, will reduce the amount of milk in the udder, relieve the pressure and make her more comfortable. Mastitus doesn't always result in failed teats, so don't panic about that at this stage.
Karen x