Oh I didn't know that. I thought she'd be stressed if I took both lambs away.
She will be, but if you want her to continue to care for both it may be for the best. Keep putting them back with her though, every few hours or so.
My lamb is still on about 50ml at a time. Won't suckle from the bottle so I'm assuming she can't suckle her mum even a little bit?
Don't assume she won't suckle her mum just because she won't take the bottle. She may not take the bottle because she's not hungry, having been suckling when you weren't looking.

Best to look at her tummy - if plump and convex, she doesn't need feeding, if empty and hollow/concave then she does need some food.
Can you get her to suck your finger? If so, guide her to mum's teat and swap the teat for your finger. Note however that lack of success here also does not mean she won't suckle her mum; some lambs just resent intervention so much they won't do it if you're there at all.

I'd be making sure she had enough colostrum on day one, and milk generally on day two, too - but then I'd be leaving her long enough to be sure whether she is genuinely not suckling mum - 4-6 hours.