I just used a body pillow that I got from Costco.
I had discomfort/pain while sleeping too, when I was pregnant with my 2 kids. For me, (and each woman is different), My Doctor suggested sleeping on my LEFT side. And this helps. And, I used the body pillow to wedge between my legs and sort of "hug" it while I slept on my side.
But ALSO, when you are pregnant, sleeping flat on your back is not comfortable. At least for me. So, I often times had to sleep in a comfy chair. While upright, this was more comfortable for me. (when lying down, the belly puts weight upon the internal organs etc. and makes it quite uncomfortable).
Try to have her experiment with sleeping positions... even if it means sleeping in a chair. For me as I said, this was often the most comfortable. And I had a good ottoman to put/rest my legs upon. Or, a lazy-boy recliner might be good too. (but I didn't have that).
Oh, a great book by the way is: "What To Expect The First Year", which you can find at any bookstore or online like at Amazon. Its great info. for a 1st baby and what to expect and about development.
All the best,
Susan