How can I position bed pillows where mother will not lay over and give to her left during sleep?

I'm wondering if you could use some kind of thick bolster to block her left side. It would be pretty hard to lay on top of a bolster. An added advantage if she has her back to the bolster is that it can provide warmth.

I think you will find an adjustable bed and good mattress to be very helpful. Some have anti-roll features. Medicare covers 80% of the cost. Get an Rx from the MD.