Hi, I'd like to help you with your question.
I am so sorry for your loss. I understand your grief and the need to do something to help.
When someone you love and cared about dies by suicide, it is very common to feel guilt. The people left behind feel like they could have changed the situation or done something to make the person better. But when someone is determined to kill themselves, usually there is little that can be done. Even therapists lose people to suicide, and we are supposed to be the ones to prevent that from happening. But it does happen even when you try all you can to stop it.
It is very common when someone decides to kill themselves that their mood lifts and they seem almost happy. It seems to everyone around them that they are doing better and there is no need to worry anymore. It is because the person feels settled with their decision that they stop feeling depressed. And that is a very hard thing to detect, even for professionals.
When your friend sent you the text, there was no way to know what she was going to do. Even if you knew your friend felt depressed, it is not always possible to understand someone else's plans or understand what they intend to do. Even if you decided to talk to her, her phone call may have been a way for her to say goodbye, without you knowing. You talking with her would not have made any difference.
It is very common to feel the need to do something to help. By all means, go over to see your friend's family. Take the bread over. They will appreciate it. Tell them you are sorry and let them talk if they want. There is little more you can do beyond letting them know you are there for them.
You will experience a time of mourning. That is normal. Educate yourself on the stages of mourning and be sure if you feel you cannot work through your feelings, you seek help. Talk to a therapist or your pastor, if you attend church. Faith can help you heal and find comfort.
Here are some resources to help you get started:
Grieving the Death of a Friend by Harold Ivan Smith
Grieving a Suicide: A Loved One's Search for Comfort, Answers & Hope by Albert Y. Hsu
Silent Grief: Living in the Wake of Suicide by Christopher Lukas and Henry M. Seiden
You can find these books on Amazon.com or your local library may have them for you.
I hope this has helped you,