Hi Bridget,
I posted this in the welcome thread too, but I'll post it here as well.
My mum is a vet, and I'm going to ask you a question which she always says about goats and sheep. After the first 12-24hours, if you watch a sheep or goat behave naturally with its lambs or kids- Does it stand up in the middle of the night in order to feed the lamb/kid?
The answer is, no it doesn't. The only way you get it to take more milk at a time is to extend the gaps between feeds, so it gets hungry.
As to question number 2, if the sheep really likes the lamb, I'd leave it with her. Or if you want to be extra safe, make it a tiny pen insde its mum pen.
And Welcome Smiley
Beth