First you should absolutely feel free to contest my advice. I kept a ball python for a couple years before he died of cancer. I'm no expert. Most of what I know I read on this forum.
That said. In my non-expert opinion, you need to lower those temps because you're risking a burn. Just because she hasn't burrowed in the few months you've had her doesn't mean she won't. Ball pythons can get burned by surprisingly low temperatures. Burns can kill. Even if it doesn't, you don't want to have to treat a burn. It'll be miserable for both of you.
Maintaining ambient temps using UTHs isn't going to work in a cold basement. I suggest you either move your enclosure somewhere in your house where the ambient temps are higher or start using a heat lamp. Setting up a heat lamp in a plastic enclosure isn't easy but it can be done.
Whatever you decide to do, I want you to know that I'm rooting for your success.