Oh boy, I feel for you. Your daughter is of age to make that decision, although i understand mentally she isnt, if you push her she will say you made her do it and hold it against you for ever.
Has she got a health visitor who you can discuss together the problems.
I am a foster carer and the baby I have at the moment was born to a mum who couldn't cope. She gave it a whirl and did ask social services to help. In the end she couldn't commit to him so he is now being adopted. There are no hard and fast rules to when you decide to ask social services to help or keep them as long as you show you are trying. If it gets too much and you feel the baby isnt being looked after sufficiently then you need to step in and get the authorities involved if you dont want to take over. If she does decide to try then you have to step back and let her see for herself how difficult it is and then she can make the right choices. If you have health visitor you need to mention the fathers family and their problems and she will keep a good eye on the situation.
Good luck.