My Mom has also experienced increases in her CA 125 levels after chemo. The doctor said that during the first couple of rounds, the levels may increase. It has to do with the way the tumor and the blood are broken down by the chemo (I can't remember the term he used). He told us not to worry about the levels because her body is adapting to the chemo. He also suggested a Pet Scan for my Mom. Looks like they are on the same page.
Unfortunately with this wretched disease some chemos work and some don't. Also there are chemos that work slowly. So her count may go up and then start coming down after a couple of months.
That's good that she is going for a Pet Scan. It sounds as if she is being monitored closely.
All of us on this forum compare chemos. It is very helpful. A certain chemo may work well for someone and then not work for someone else.
Good luck with your Mom and I wish her well.