If it's twin lamb use Ketosaid, its the best thing there is. Also try to tempt her to eat with some ivy.
If it's mastitis, then betamox l.a and metacam is best.
If she has had twin lamb, she may just be low on milk, maybe top up the lambs for a couple of days, get her eating well. The thing is if they are low on milk, it can lead to mastitis as the lambs hang off them too much chewing the teats.