The part that worries me is the "She has admitted that if this were a typical mono relationship she wouldnt feel ready to have a baby with Dh."
Not to deny that new mothers need and deserve support from their loved ones, of course they do. But unless a couple makes a commitment to create and raise a child, you can't genuinely rely on everyone to be committed after the fact. I think that's why so many relationships end within the first year of baby's life. Relationships are a lot of work, and babies are even more work. If the relationship isn't on ultra-firm ground, then something's going to give out. Since by then the baby is already born, and people don't tend to choose adoption as an afterthought, it's usually the relationship that falls apart.
What LR says about being positive definitely makes sense, if it is your desire to create this family and bring this child into the world. But if you all go into this as a call of duty, I don't see it being sustainable.
Of course, this is all based purely on the frightened, hesitant tone of the post, and not generic advice for any unplanned pregnancy. If everyone find themselves excited, after getting over the initial shock, then that's great. Bring on the balloons!