Okay...
'the boy'. He's not a boy, he is a man. Even if he obviously wants to be a child and not take responsibility for a new life he helped bring into being. Treat him like a child and he will most likely act like one. And your dd may get riled...if he's a 'boy' she must be just a 'girl' not an adult about to become a mother for the first time.
Also made me at 'we have not met the boy and didn't even know she was seeing anyone'. She may have wanted to keep it private that she sees men and doesn't marry them! I would not have told my family how many men I did or didn't see...let an adult keep what she wants private.
Also...how to manage financially, 'money is very tight at out house but we have to support her whatever!' she can manage that as an adult. Help her if she asks for it, but she's big enough to look after herself now (and old enough to get pg and decide to keep the baby!) and more than capable of talking to social security and asking what she is entitled to.
I feel concerned you are treating her and the father to be, like children. Just take a deep breath, think back to how you were when you were pg at around that age, take a fresh look at your dd, she's a mature adult now, capable of having a baby, coping and looking after herself financially. And I guess you may also have told her how hard it was to be pg at that age and she's been a little child and done as you told her not to do...but we only learn from our OWN mistakes, not others, not even our mothers.
On the positive side...'I told her everything would be fine, and not to worry' that bit is great! I understand you are worried about her future and money, but LET her have the responsibilities of a parent to be, that is to worry about HER future and HER finances. If she needs help she will ask.
Having said all that, I have no experience of any of what you have talked about so feel free to ignore my advice