I think she needs to get a scan to find out how far along she is first of all.
And then you all sit down (you, her dad and dd) and ask her what she wants.
If she has goals for further education then while having a baby shouldn't stop that, it's going to make it extremely difficult without a lot of support, both physically and financially from you both.
She cannot claim any benefits for the baby until she is 18. And if you don't meet the threshhold for tax credits for your children then as she is living at home then it's unlikely she will qualify either as she will be deemed to have financial support (although not 100% sure, you will need to check that out). Child benefit could be paid to you or her.
Other than that, she's unlikely to get any financial support from the Government. She will have to look at going to college or work to support her and the baby and use childcare.
I think if you started a thread asking for honest opinions of life as a young single mum on here on your dd's behalf that could make her see that having a baby is not that easy.
Some young women cope very well, others need massive support.
Whatever decision she makes, it's good to know you are going to be there for her.