I hope it is scar tissue but I am concerned that it got bigger? Seems like scar tissue would dissolve. Sometimes they develope a hernia at the spaying site b/c that area is fragile until it heals completely. It isn't serious but I know what you mean about not wanting her to go through surgery again.
I am sorry you can't get an answer until the 27 b/c the worrying is going to be the worst part
It will help you to know what you are dealing with and be able to make plans. If a surgery is in her future I hope you can postpone it until something like teeth cleaning is due.
Let us know how this turns out.
best wishes