Some mums can raise triplets fairly easily. If you creep feed the lambs I'm not sure I'd suppliment the milk unless there was a problem. I pull the grain off mums the day they lamb and give them half what they were gettign the next day. Its just to reduce the odds of acidosis, as the ewe suddenly has lots of room after birthing. Make sure she has lots of water and a good mixed hay, not pure alfalfa. My only concern (just a thought really) would be milk fever (calcium deficiency) so watch for her going off feed, trembling or startling easily, as early signs.