Hi Franki--
First, your T is right...it's completely your choice. There's no right or wrong answer beyond you deciding what's best for you.
I was in a similar position a few months ago. I also pay out of pocket and get some reimbursement, but I really couldn't afford to go to twice/week at the same rate. My T very kindly offered to reduce her fee to something that would be affordable. (Is that something you think you could ask about?) I felt all sorts of conflicting emotions about it, but in the end I saw that once/week really wasn't working as well as it could, so I moved to twice. I'm so grateful to my T, and happy to say that I feel like it's made a huge difference to the speed of my progress. So while I'm paying more each week, I really do think this has the potential to cut big chunks of time off of what would have otherwise been the length of my therapy.
Please try to remember that your T is trying to be helpful and to help you get the best care she can. My own impression is that Ts don't offer more than we need, since their ultimate goal is for us to not need them eventually. Still, if she thinks it can help, and if you can find a way to make it work, I really hope you'll give it a try. You can always go back to once/week if it feels better to you.
Take care!