I think the OP needs to take a step back and think a little.
OP what would your advice be to a woman of your age, a friend, with this going on?
You say that you will struggle financially.
How?
Do you mean by buying baby stuff?
Where will the baby sleep? In your ds room? Will its waking at night disturb your DD2 and her studies?
And when the baby needs a bed, not a cot, what then? In DDs room still?
How will she continue her studies?
Will she?
what about her health issues? Are they sorted now?
Can she resit her year missed at school?
How will she access childcare if she goes back to school, work or college?
who will pay for that?
Are they able to rent a flat on her boyfriend's income?
what are their plans as a couple?
They can't even drive yet, so how will they see each other when the baby arrives? Bus? Taxi? Parents doing the taxiing?
Has any of this been discussed?
You have been very vague about how this will play out.
Maybe you as well as your DD need to have a good old think about what will happen in reality.