Don't pull the placenta, it will come out on its own. If you try to pull it out it could break off and a part be retained. If she is crying for her lambs, you can try putting the sac from the one that is still in it on the rejected lamb to see if she will accept him. Does she have any milk? See if you can tie her up and get him to suck. You might get lucky and get her to accept him. How old is he?
All the lambs look small. Pretty colors. Such a shame. Since you didn't know how far along she was, they might have come slightly early. Also depending on the part of the country you are in and the type of hay or grazing they had they might have been low on selenium or some other essential mineral that would cause them to be born early or very weak. Call your vet and ask who would perform a necropsy on the triplets.
Having triplets at 11 months old is a lot for such a young ewe. However the fact that she cleaned them up, is a sign that next time she is bred she will be a successful mom.
