It's good that you are giving her the support of a friend. When she tells her parents she should just tell them how it is and say that although they may be upset with her for the pregnancy, what she needs more is help, love, and the proper care. Most teens don't even want to be where she is in the first place, so it is enough for them to be in the situation without the parents being upset about it.
If she feels too scared to say it in person to her parents, she can write it on paper and give them the news that way....and in the case of parents who are not very understanding, this way she will be able to say all that she needs to say.
Once her parents know, and as long as they are understanding, a lot of the pressure and worry that she is feeling is going to greatly subside. It is arguable that the BF would have any custody rights at all since he is a minor and cannot provide child support. It is a good decision that she give the baby up for adoption, or maybe perhaps her parents would love fostering child as well.
There are many options to be considered and she has a lot of time to think about what she wants to do. She just needs to know that is isn't the end of her world and that there are many others in the same situation as she is and that there is help for her.
IF she is getting too depressed, you should tell her parents or a counselor because depression can be very harmful and deadly....so just keep a look out for her.
You are a good friend to her, so keep up the good work.