M.,
My daughter is very young, so I haven't experienced this from a parent's point of view. But, when I was younger I put my parents through a bit of hell, so I thought I would chime in.
1) Understand that this is about her, not you. Regardless of how heartbroken you feel, don't blame yourself when you're talking to her. Talk in terms of action, and ask her questions - open ended questions- about her situation. If she's forced to think and talk through the situation, you might find that she gets a better understanding of just what she's done. For example, if she's pregnant ask her how she's going to support herself and this child without getting emotional. Don't fill in the blanks, just get her to think about it.
2) Don't tell her she needs "help" but ask if she'd be interested in talking to someone objective - a professional can be of great help in a bad situation and can help her sort out why she's making negative decisions that will adversely impact her future. A lot of kids will object to seeing a therapist if they feel like you're telling them they're crazy, but the reality is that she'll likely get a lot out of talking to an objective adult that isn't you or another authority figure. Someone they can say anything to. Make an appointment for her and take her there. Tell her that you feel like you're too angry, heartbroken, or whatever you're feeling to communicate with her the way you want to and that you want her to feel like she can talk to someone. That you hope she'll approach the therapist with an open mind and heart. Consider seeing a therapist together to mediate if you are having trouble talking to her without fighting. Consider seeing a therapist yourself so that YOU have someone to help you figure out the best way to approach the situation and to help you get past the hurt and heartbreak that you're feeling so that you can be a strong support for your daughter.
3)Find resources. No matter what her situation is, there is probably an organization that can help. Don't treat this as though you want to "solve" the situation, show her that whatever the scenario, nothing is hopeless, by being proactive. When you find resources that can help her, make the appointment for her, be there to support her, but don't speak for her, she needs to own the situation and its outcome.
These are my personal opinions, and there is no right way to parent. Kids don't come with an instruction book, and they'll surprise you every time with their behavior and point of view. But, this is my advice without knowing the details of your situation. Good luck, and know that you are a good mother with good instincts and lots of love for your children. You will get through this, and the pressure you feel now has the ability to enrich your relationship with your daughter in the long run if you look at it as a positive possibility for growth in your relationship with her. Easier said than done, but possible.
Much love and hope to you,
T.