Thanks for the extra info:
Sounds like she might have an infection of her mammary glands. This is something that can occasionally happen. I would take her into the vet so they can assess her and possibly get her started on antibiotics. It is important for her kittens to get milk, so the sooner you can get her fixed up the better. You can try some warm compresses in the meantime, if she will let you (water balloons filled with warm water work well).
Good luck! It is definitely kitten season (spring). Thank you for being a concerned owner. If you feel this answer helped you, please accept. If you need more info or have more questions, just reply.
Sincerely,
Dr. Amanda
Dr. Amanda
Small Animal Veterinarian
Special interest in canine and feline behavior.
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