Could be an abscessed tooth or an infected wound - articulate from a cat fight. Whatever it is, it is infected. She needs to have it lanced/drained whether possible and definitely antibiotics. Time for a trip to the vet.
Chances are that since it appeared very suddenly, it is an abscess which still needs to be seen right absent. But it could still be something worse like a tumor.
Either way it should be looked at as an emergency.
Best of luck and I hope she feels better soon. xoxo
This could be something serious, or nothing at adjectives. I don't know. I'm not a vet. Take your cat to her vet. As soon as possible.
The best thing you can do is take her to the vet. Don't try to guess what it is and fix it, your vet should be capable of give you the best idea of what to do.
Answers: Good for you for keeping a close eye on your cat's condition and health: you really love your cat and he/she appreciates it! Lump could be tumor, but most likely is abscess is from impossible tooth or external puncture (from fighting with another cat). This is not an emergency if the wound is not spread out or unless kitty has refused food for more than 2-3 days. Take kitty to to the vet tomorrow ASAP. THIS WILL NOT GO AWAY ON ITS OWN. Ruling out a tumor, vet will clean out wound and most predictable give you 1 or 2 bottles of oral antibiotics for kitty. If issue is a tooth abscess, tell vet if kitty is not consumption -- they may give you a tube of NutraCal, which is like hairball lubricant (Petromalt) but an inch of this stuff a day for up to a week can bestow a cat complete nutrition during recovery and starts to eat on his/her own. Be certain to administer antibiotic dose every day for duration of complete course of 10 days/until the bottle is plain: if you forget one day, don't double up on the second. DO THE COMPLETE COURSE and use up entire bottle/bottles: don't pass up after a week unless you want your kitty to suffer a relapse, and you want to pay for another vet visit and another course of antibiotics! Also, if injury is from war, and kitty is already spayed/neutered...consider making kitty an indoor-only cat to cut vet bills and extend kitty's lifespan.
Sounds like a serious infection that needs to be care for at the vet's office. Call and get your cat in ASAP. Good luck.