Oh dear. Poor you OP. What an utterly hideous situation to be in. You have my every sympathy.
There is so much good advice on this thread, I am on the side of the pragmatic and harsh, to be honest. However, I do have deep deep empathy with your DSD.
I think perhaps her whole ideas and skewed because of her mother buggering off years ago. No matter how lovely you have been to her, she has had to face up to the fact that she was completely rejected and thrown away like a piece of rubbish by her own mother.
It is possible that she deliberately (almost without knowing it) got pregnant, in order to have something of her own to love, and a baby who would love her most in the world, and to recreate that love which she has lost from her mother. That's what I did. My mother didn't raise me, I had a rotten childhood, having my daughter (albeit young) was a hard headed decision which I made. However I was 17 when I had her, only three years older but light years away in terms of how it impacted my life.
I would say that abortion would be the best thing for your DSD - however it may well be that she wouldn't be able to consider it, it may well be completely anathema for her to consider getting rid of it. She is probablt looking at life through rose tinted glasses.
My daughter is now 14, I never have regretted for a moment having her, she has been the light of my life, however it was SO bloody hard practically. That said, I raised her on my own, having her did NOT impact on anyone else, which is the hideously difficult aspect of the situation you are in. I have said since dd was able to understand that she will go to school, go to uni/whatever, and if she gets pregnant at a young age she will have an abortion, she is not to go through that same as I did. I think I am justified in saying that, my dd has had a completely different upbringing than I have, there is no need for her to have a baby because she has nobody else to love, or who loves her. It would truly be a nightmare for me if DD got pregnant and wanted to keep it.
I do agree that it would be an impossubkle thing to send your DSD to a mother and baby hostel, no matter how (in a practical sense) I agree with the sentiment.
Oh god I have nothing useful to say. I feel so sorry for you OP because if she does have the baby it will impact on your whole life. I don't know what to advise. I just hope to god that she changes her mind and wants an abortion. Such young motherhood should never be encouraged.