If you’re an experienced lamber then I’m sure you will have, but have you tried thumping the underside of the Ewes udder? You will have noticed that Calves and Lambs all head butt their mother’s udders prior to feeding; this is a trigger to milk let down.
In the past I’ve found that first time mums, especially with first time colostrum, are reluctant to let their milk down.
I’m afraid this could be just the start of your problems with this Ewe as there is a good chance she will now reject her lambs.