Hi!
Your LO is very young and it's normal to need night feeds at this age and go back to sleep on the boob but to sleep for such a short time after the feed and to be grunting and whining is very disturbing for you and get.
Sounds to me like she might have trapped wind. Sometimes LOs want to keep sucking to relieve that.
Do you burp her well after the feed? (Tricky at night I know but worth it).
Can you have her upright for a little bit before going back in the cot?
Have you experimented with feeding positions to see if there are any to reduce amount of air swallowed on feed? (Sorry it's a while since I was BFing a newborn my kids are 1 & 3 now, I can't remember exact advice on feeding positions to help with wind)- but maybe someone else can advise...or a Google? I think we used "biological nursing" where you place LO on it's tummy on your chest to feed rather than cradle hold and that and help reduce wind.
My DSsuffered bad trapped wind and discomfort, especially with NFs and we did get some medication to use before feeds for him but I know that not everyone wants to go down medication route with a you d baby, but if you do, talk to add or pharmacist for advice.