Welcome! Pictures!
My guess is that she's hiding from the 7th graders. They're much larger than she is and a lot more active and snakes are prey to a lot of things larger and more active.
This seems especially likely if she's more active in the summer when she's living with someone who isn't a slightly psychotic pre-teen. (I teach 9th graders -- they're all nuts!!!)
My garter's second favorite hide is a plastic container large enough for her to get her whole self into with a bit of moss. Her first favorite is the aspen chips that I use for substrate. But then you really wouldn't see the ribbon -- that also might be an issue because you'd have to move her to another container to feed her to make sure she doesn't ingest any of the aspen chips.