Hi, I’m so sorry to hear that you and your bunny are going through this. Especially since she has been with you for so long and seems to otherwise have a very happy life in your care. I have never experienced this myself, nor do I have any background with this type of medical care, so I’m sure others on this site will reply with their advice.
Unfortunately, I have seen a lot of instances in other rabbits going through abscess issues where it has become a long and winding road of surgeries and flushing of the site as it is common for them to grow back quickly. Rabbit’s have a a very thick material in their abscesses which makes it difficult to fully clean and remove the infection.
There have been stories from other members of having abscess material removed, either with surgery or debridement, with successful results, including no reoccurance. So don’t be afraid to try, just keep in mind her age and a history of problems with her spay surgery can increase the chances of complications.
You will know what is best for your rabbit and any decision you make will be the right one. Sending healthy vibes. <3.