I've had several ewes this year with little milk.
What is her bag like and how are the lambs behaving? If they are hunched up then they aren't getting much from the ewe. Sometimes they will drink from a teat, and then swap sides if the ewe is low on milk. If they are sleeping a lot, but when distrubed get up stretch and drink from the ewe, they are probably getting their milk from her.
I took one lamb off the my ewes with little milk as after a week or trying their production didn't improve.