Hi OP, my thoughts are with you at this time. It's not the end of the world, whatever DSD chooses, either way.
You say you don't remember seeing any signs of her using sanitary products for 2/3 months. Is that right? If so, I hate to sound pressing but she's going to need to consider antenatal care if she does want to keep the pregnancy, she could be coming up to 12 weeks+.
I would've been in the same school year as your DSD, I think. I am 19. I'm pregnant.
However, I don't think I could have been able to have a child in your DSD situation... I'm quite old at heart and I do have a fair set up. DSD sounds as if a lot of financial and emotional support would be required from the family, is this correct? Not only that but she sounds as if she quite enjoys her youth and has things like Uni on her horizons. I left school at 16ish and I'm very fortunate to have a very well paid and stable job now.
I am getting married in August, DP is 25 so quite a lot older and again well settled with a good job and our own home.
Is this something your DSD imagined for herself and really wants? Does she want a 'family family'. What are her expectations from this situation, if she decides to go through with it?
These are all things to go through with her.
I don't think 18 is extremely young but the initial set up of an 18 year old often isn't great, if that makes sense:
Whatever she chooses to do, you sound bloody amazing. As does your DM.
Good luck with anything and everything 