Been there, done that, have the t-shirt (2 survivor tshirts now :) ) Here are my suggestions:
1. Make it long enough to tuck under chin to under heels.
2. Make is wide enough to tuck around her when she is in a recliner.
3. Use flannel as a backing and no batting. Make sure to wash the flannel in HOT HOT water and dry on HOT before you put it on the back. The quilt will need to be washed many times and put in the dryer as well. You dont want to make a heavy quilt. There were days when every thing hurt even the touch of a sheet. Having the quilt light would be best and easier for her to carry as well.
4. Put her full name on the quilt some where easy to see. If she is in the hospital it may accidently get put in the hospital laundry and this way it would be easier to return to her.
5. Take pictures of the quilt front and back before you give it to her...see #4 above.
6. I agree with the no pockets and make a tote instead that the quilt and a notebook and full size calendar would fit into. Its hard to keep all the appointments straight and what each dr/nurse/tech said.
7. My friend's 11 yo daughter wanted to make me something and my mom helped her make me a pillow. It is 24inches wide and 18in top to bottom. Just out of fleece with 4 layers of fleece in the middle and sewn around the edge(she hand sewed it had to use an ice pick first) I have been using it for two years now. I dont get in a car without it. I place it under the seatbelt and it keeps the seat belt off my chest and shoulder. My surgery site and area where chemo port would be located. It gets washed every week and is getting a bit "pilly" but it is wonderful. HINT. I had to tack the 4 corners and the middle of inside fleece after I washed it the first time because it rolled.
7. Thank you for doing this for her. You are all in my prayers.