I don't think that all that fuss is necessary. The baby is obviously feeding well. I think its pretty normal for them to be sleepy for the first 24hours anyway. When I had my baby, she slept for ages, and didn't feed too much, but the nurses weren't worried. Just said to keep an eye on her colour to make sure she wasn't going jaundice and an eye on her nappies.
Congratulations to your sister, I think she is doing a wonderful job! Tell her to tell the nurses to bugger off lol