I was at 22 in your DDs position so I am doing the 'with the wisdom of hindsight' thing about what I would have liked my DM to do/say then and today I have DC of similar age to yours so I am feeling your dilemma as a mum too. I know I would want to encourage my DD to make what I would think is the right decision for her - but I can also see that what I think would be right might not be best for her in the long run. I simply cannot know. Only she can.
So, in your position - I'd sit her down and say that having thought about it, I strongly believe what I am about to say to her and that I won't change my mind - because she really needs to believe what comes out of your mouth next.
Then I would say - I love her more than anything in the world and I will always want the best for her, which is why I can't tell her what I would do. It's her decision to make alone.
This is/ may be the first major decision she will make as an adult and its a big one but she needs to make it and know that whatever decision she makes you will support 100%.
She may cry, plead and say she doesn't want to hear that from her mum but you must try to stand firm on that.
I would try to use neutral language at all times when discussing each option so as not to give her huge hints which would undermine her coming to her own decision.
Whatever she chooses SHE is the one who needs to be 100% sure she is ok with it as she is the one who will live with it. And to that point her bf's thoughts are now interesting but ultimately irrelevant on this matter.
I would take time to make sure she knows that she needs to separate out the two things (bf & relationship and pregnancy) and deal with each one separately.
- I am pregnant do I a) want to abort or b) have the baby.
I'd want my DD to feel that which ever she chooses she would have me on her side and that I'd be proud that she made the right decision - for herself.
- What will happen to my relationship? Answer - who knows but as two adults they will work that out between them whatever decision she makes.
One thing I'd want my DD to think about is that regardless of what decision she makes about this pregnancy the relationship will run the same course over time (they will either stay together or split up, and if they do split over this she can be pretty certain they would have split at some point in the future). That's the truth really and she needs to go into this understanding that adult relationships are full of compromise and contradiction.
Then I'd ask her if she knows where to get independent advice to help her come to her decision. Brook look to be impartial and I like that they offer specific advice for under 25s but I'm not an expert on these sites so maybe your gp can tell you where to suggest.
In the end so long as she makes the decision for herself and is unconditionally supported by you - all will be well.