Had the same problem this year with a ewe (born last year) so still a bit young herself. Mothered it fine while inside but rejected it point blank, with the head butting etc as soon as turned out. As I have no other orphan lambs (and work full time so don't have the time to bottle feed) I brought both back in and put mum in headstocks (made from an old pallet). lamb can feed as mum can stand up and lay down and has access to hay and water but cant turn round and butt the lamb. introduced lamb to creep feed from week 2 and have just turned both out we are now week 6! (did turn out again in-between but ewe carried on not letting it feed and butting, so brought it back in again). lamb is now old enough and eating enough creep and grass that if mum doesn't let her feed now, it shouldn't matter, however there has been no butting at all this time on turn out, and both are grazing nicely side by side, (although have not seen lamb feed from mum, lamb has access to creep in creep feeder). it is a bit of a faf, but ewe is now on cull list as do not want the hassle next year. what you do really depends on what you have time/energy for.