OP, my fifteen (just!) year old sister put me in a very similar position a couple of years ago. There's a thirteen year age gap between us, btw.
I can recall my feelings quite well:
I was - fuming that the silly mare had gotten herself pregnant
-Impressed that she'd realised, tested and thought about what she wanted to do.
-
Honoured (and even more impressed) that she'd thought to trust me with the information and ask for help.
-
Worried sick about how the rest of the family was going to react, and how on Earth I was going to explain that I'd known and not said anything.
In the end, I took the course of deciding that I should respect the honesty and trust she'd shown me (and the sense - can you imagine what it must take at fourteen to even admit to yourself that you're pregnant, much less face anyone else?) whilst strongly encouraging her to be honest with our mum.
In the end, I sat next to her whilst she 'confessed', then let her escape to her friends whilst I sat and took the flak. And, yes, I did get demands of 'You knew, and didn't say anything?' but my response was that, in the short term at least, it wasn't my secret to tell and that I had to give my sister the chance.
I think (I don't know, because it never came to it) that I would have told my mother eventually anyway. But not to start with.
Have another chat with your DSD, tell her you're impressed with her behaviour so far, and explain that you think she needs to tell her dad.
Say that you'll be with her, say that you'll even say the words if you have to, but that she needs to carry on being as grown up and as sensible as she has been so far.
If your DH really is likely to fly off the handle, arrange a bolt hole for the kid over night, so that she can run and you deal with the immediate fall out.
It's tough, but at the end of the day, the worst he can throw at you is 'Why didn't you tell me?' and your answer is clear enough - 'Because I wanted to give your daughter chance to tell her yourself, as the adult she's very rapidly going to have to be, and I thought she needed a few days to get her head around doing that. It's a hard thing she had to do.'
Good luck.