Good Morning and welcome! I am Dr. Loretta, a licensed veterinarian and I am happy to answer your question.
I am so sorry to hear that Lacey is still not feeling well. It does appear, by what you have described, that this mass with pus was most likely due to a tooth abscess and this has been resolved. You said that the biopsy said cancer but you did not say what type of cancer....
It is not unusual for such a serious procedure for Lacey to take a few days to get over this. It is painful and at her age, the anesthesia can be hard on her. Your vet should have given you antibiotics and pain relievers to help Lacey past this.
For now, it is best to give supportive care but if you are not comfortable with your first vets diagnosis, take Lacey for a second opinion.....there is nothing wrong with this and this will give you peace of mind for your impending trip.
Does that make sense to you?
Please let me know if you have ANY other questions. My goal is to give you 100% satisfaction and if you are not yet satisfied, please REPLY so I can clarify for you.
Sincerely, XXXXX XXXXX
Thank you so much, Margaret, for your kind rating. It is very much appreciated! Even though you have rated, we can still communicate. If you have other questions, please Reply. I am always happy to help.
Have a wonderful day!