What First Aid Do I Give To A Cat With A Swollen, Red Nipple?

False pregnancy in cats is very, very rare.  Mammary hyperplasia usually occurs for other reasons.
However, many false pregnancies are mild and resolve over 2-3 weeks.  Stimulation of the mammary glands prolongs the false pregnancy.  Do not bath, compress, or rub the mammary glands.  Do not allow the cat to groom herself, suck or lick her nipples.
Nipples to not usually become red and irritated--this may mean an infection is present.  Your cat needs to be examined by a veterinarian to diagnose the cause of mammary enlargement and see if any treatment is needed.
If the false pregnancy is not self-limiting or seems severe your veterinarian will be able to assist you with further treatment options.

You are going to have to take her to the vet. She could have a blocked duct, that has gotten infected. Hope this helps, good luck.

You could try bathing the area regular if its clear discharge then it might not yet have become infected if symptoms persist I would get a vets opinion