Op, this must be very hard for you and her Dad: your little girl going through this and fast racked into adult experiences.
The process won't be easy for her, so support her through that.
But she has made the best she can of an accident any sexually active person can experience.
She seems clear about her decision, so be careful not to project your own reluctance to terminate on to her. It is great that this is her decision and you have not pressurised her to terminate. The fact that it is her decision will probably mean the emotional fall out is minimised.
She may regret that the pg occurred, but for many women, me included, the ending of an unwanted pg comes with great relief and no regret. Be careful not to imply that she ought to feel guilt, regret and need counselling.
I felt almost indecent because I wasn't having this emotional turmoil about a 'difficult ' decision, and as if I would be thought an immoral, callous monster for admitting I felt huge relief and no regret except some sorrow and poignancy (for which I did not need counselling!).
Many women feel that they cannot say this. I have read articles by women who feel like me.
Be careful not to make her feel she 'ought ' to feel guilt and regret.
Your dd has a boyfriend who loves and supports her, I hope your DH can find the rational response and allow him into the house to give the support for the mistake he was involved in.
She will feel very hormonal and may we'll be very emotional, especially with her bf going away.
It is not a situation anyone would want to be in, but hopefully your dd will now move on positively with her life, in control of her future, her educational and relationship opportunities, and the time at which she becomes a mother.
Good luck to all of you.