Sorry to hear your trouble Declan, don't beat yourself up though these things do happen.
Personally i would keep the ewe out of the lambing field we have had such ewes be an absolute pain when other ewes lamb, sometimes they miss their own dead lambs so much they will steal another ewe's lamb or a newborn will get inprinted on her and she may have dried back on milk. so i would find her a place to dry off somewhere with not too much grass or even keep her in for a day or to on hay.
If of course you have something you can foster accross then go for it while she still has colostrum but this will only be there for 24 hours or so and you may have to milk her to get it going.
Another action if you have the time is to milk her and freeze the colostrum for use in the future then dry her back.