My 7 week old DS does most of his nursing at night too. We co-sleep, I end up sleeping through most of it. I still manage to get a good nights sleep, I actually get more sleep now than I did when I was 9 months preg.
We sleep on our sides, tummy to tummy, with DS positioned so he can latch on/off by himself. Usually he wakes me up when he roots around and latches on, but not always, sometimes I sleep right through it. If he does wake me, I usually fall back asleep after a few min, and he nurses himself back to sleep. Once or twice during the night, he'll fuss, and its bc he wants his diaper changed. Sometimes I do it, but a lot of the time DH does it so I dont have to wake up/get up. DH scoops him up, gets him changed (we dont talk to him, or stimulate him in any way during night changes bc we want him to stay as sleepy as possible) and sets him back down next to me, and I get him latched on. Everyone goes back to sleep.
I'm not sure what 'system' your friend has going, but maybe this would work for her? I know I get very depressed and moody with no sleep, and I feel very very lucky we are getting the sleep we have been. GL to your friend!