You need to have your kitty examined by the vet. Although rare, spayed cats CAN get mammary cancer and the sooner it is diagnosed, the more likely treatment will be effective. The one thing about mammary cancer is it is relatively easy to remove and the success rate is high if taken care of early. This could be something entirely different, but having her checked is your best bet. Please let me know if I can help further.
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Lori McLaughlin
Your veterinarian should ALWAYS be consulted first and foremost when your pet's welfare is at stake.