Wow! Do I have some advice for you! :)
I am a little older than your daughter (27), however, when I became pregnant, I was left on my own immediately. (My daughter is 19 months now) I did have a full-time job and my own place to live, but I did not make enough money to support both my baby and myself. Thankfully, my parents let my daughter and I stay at their house for a while. The thing is, if she lives with you after she has the baby, she must realize it cannot be a permanent situation. She as a mother will need to get a job and support her baby and it's needs as that is a single mother's job. Too, after a while, no matter how big the house, it becomes cramped for both the grandparents and the mother. Moms will always be moms which was difficult for me because my own mother forgot that i was my daughters mother a lot of times and over stepped her bounds. I never said anything of fought about it, but you understand how the situation, whether in the open or not, could be difficult and stressful for all involved.
One huge thing is, though... I understand where you are coming from, but please don't suggest to your daughter that she abort her baby because of her current life situation. Although I was left on my own and struggled at first, my daughter is my world and I need her just as much as she needs me. My daughter really saved my life. Perhaps the baby will make your daughter realize what she needs to do in life and what she needs to do for the baby. Just make it clear that she will have to get a job, find a sitter/child care and be prepared for the responsibility that it is. I love being a mother, but you know too, it is not just fun and games. Babies grow out of the cute baby stage eventually and she must be prepared for all that is to come. Your daughter also needs to know that she cannot just leave the baby with you whenever she feels like going out for fun. I could see that being an issue when she turns 21. Maybe, but hopefully not. She just must understand it is HER responsibility to raise the child that she delivers, that she created.
I don't know your daughter or you. All I know is that I love being a mother and thankfully, I'm not married because it would have been a mistake this far. Being a parent, especially a single mother can be very tiring, though. 5 days a week I drop my girl at her sitter's house, drive to work, put in 8 hours, drive to pick up my girl, go home, fix dinner, play time, bath time, book time, talk time, bed time, then I clean my house each night because with a little one, I cannot save it all for one day. Then there's sleep - if I'm lucky.
Also, I don't know the biological father of your daughter's baby, but for the baby's sake, she should not cut him out of the picture desite her feelings. If he does not want or just will not be around, let that be on him so that the baby will not grow up to blame her mom for not knowing him. Your daughter should also file for child support. If she does not get a job and applies for assistance (even if she does get a job) I believe the state will seek out the father anyway so that the father has to support the child that he created instead of the state supporting it. Just because he has to pay child support does not necessarily mean he has to be in the picture if he cannot be trusted with the baby's life.
There are several programs to help single mothers. I don't know where you are from, but check on line to see if there is a C.A.R.S or Healthy Families program in your area. Also a lot of hospitals offer classes to single parents as well as group support. There are programs to help with child care, and of course food stamps and medicaid if necessary and the W.I.C program is excellent. I have used W.I.C. and Health Families (which isn't only for single or low income families - they offer a list of many, many useful resources from docs and lawyers to family activities and advice and information on physical and mental developement - anything you need really) It is not always easy to get help, though. It all depends on your income (so they say). These are just some helpful options that are definitely worth checking into now to start planning for the future.
I hope my advice helps your decision and your daughter's. Good luck and may God bless you.