One thing that really helps, Josie, is getting her reclined and her legs up. If she could have pillows against the arm of the sofa, her head on that end against the pillows, and her legs up with a pillow under her knees, she'd have the pressure points changed up. That's what I basically do in my power wheelchair when my "sitter" needs help desperately. I recline and tilt, so that the weight is on my back, with my feet up.
Another help is a "donut cushion". If you look at Amazon, there are some with blue covers, and are very comfortable (soft foam rubber) as well as inexpensive. Her cushion she presently uses sounds like a "tailbone relief" pillow. The donut I have takes pressure off my "sit bones" and onto my tailbone (think of the three bones as a triangle).