Hi, thank you for your question about your rabbit.
I'm assuming everything else is okay with her - she is eating okay, acting okay etc? How old is she?
There are a couple of possibilities that I think of with this information. The first would be an abscess. This is an area of infection (pus) and could be from a wound possibly. The fact that you says it moves with her skin is a good sign. If it is small and not due to teeth problems, it might resolve with a minor surgery and antibiotics.
The other possibility is also an abscess, but this time due to her having tooth problems. Rabbits teeth are constantly growing and it is why they need rough, fiber like food (hay) to eat. This helps their teeth. Sometimes their teeth roots will become infected and the infection will show under the chin as a lump.
This type of lump is much more of a problem and may need surgery and long-term medications.
Rabbits can also possibly have tumors of their skin that would show as a lump, but this would not be as common.
In order to determine what it is, she will need to see a vet. The vet will examine her thoroughly and they should do a good oral exam to look at her teeth. They probably will recommend an aspirate be taken from the lump. The aspirate will take out some material from the lump and they can look at it to see if it looks like pus or not. If they are suspicious of a problem with her teeth, they may recommend some radiographs (x-rays) be taken of her skull/teeth.
I know this does sound like alot, but I would assume that most exams would cost about $35-$45 depending on where you live. An aspirate would be probably be about $25. From there, the cost will vary depending on whether they think it is her teeth or not. If it is a tooth root abscess, the best treatment is often surgery, however, sometimes long-term antibiotics will work. Since I'm unable to diagnose her online, I would not be able to tell you the cost of the surgery etc. without seeing her.
Almost all veterinary hospitals will accept credit cards and if needed, many also work with a credit company called CareCredit. You can apply for this right at the vets.
At home, there is really nothing to do except to watch her closely and make sure she is eating and acting okay. I would not give her the Petramalt, as this will not do anything for this.
Please go to the rabbit website www.rabbit.org
. They have many discussions on their site under "health" about abscesses. If you do not have a rabbit veterinarian, they also have a vet look-up list. If you let me know where you live, I can possibly also help with a veterinary referral also.
I would encourage a vet appointment sooner rather than later as rabbits are often very good about hiding the signs that they are sick. Please let me know if you have other questions and how she does. Thank you.