As per the history, the issue seems to be due to gastritis or acid reflux. If pain occasionally gets severe enough to wake her up from her sleep, she might have ulcer in her stomach.
If it's there since a few days, its probably gastritis, and if it's there since long, she needs a check-up.
Next Steps
For now, take over the counter antacids like Pantop-D once daily for 10 days.
Consult a physician in case the problem persists.
Health Tips
Slow the speed of eating, do not drink too much water while eating, keep at least one hour gap between dinner and bed time.