Place a hot flannel on the affected teat (as hot as possible without it burning her of course) hold it there for approx 2 or 3 mins try and extract a little fo the milk, do this 2 or 3 times a day as well as getting the stronger bigger pups to feed on this teat. The swelling should go down, it could be the begining of mastitis so keep an eye on it..normally the hot flannel works a treat if you catch it early.