Head/neck rubbing and making rough patches?

My dumeril's boa has these scales sticking up on her heck and the spine of her neck for the past month or so. They feel scratchy to the touch. Her humidity is at 50% consistently and she always has complete sheds, so I figured it's not stuck shed.

Someone concluded in another group that she's rubbing her head/neck on stuff in her cage. I had taken everything else except for her water bowl, hide, and aspen for quite awhile already. So I figure she must be rubbing on the sides and top of her tub, where there are ventilation holes.

She's been in this same tub enclosure for the past year, and the scales sticking up or the rubbing only started recently. So I was wondering if there's any way to help stop it, and why she is doing it?

She's in a 110qt sterilite tub... She's too heavy for my scale, but her length is almost exactly 5 feet and a couple inches.