Sorry you are feeling down and about the loss of your friend.

Survivor's guilt is common. Why didn't I...? or Why am I here and not her?

Some specific links you might like besides the grief loss forum

Post-traumatic Stress - Forums at Psych Central

Depression - Forums at Psych Central

There are also Chats for emotional support and there is a Tuesday 9pm-10pm EST -5 hours Greenwich meeting with the founder of PC Dr John. there are other groups on other nights.
Click on Chat link in middle top of page.anytime or at the time specific groups meet (see calendar)

From reading the progression of events, your friend texting you could have been a way to say goodbye. She may have already committed the act of self injury and just wanted to reach out to you but not alert you so you would send emergency personnel. It sounds like she really wanted to go. She didn't reach out for help she just said goodbye in a rather awkward way.
If you did call her, you probably would have got her voicemail.
Rather than go on with the blame game, how about writing a paper celebrating your friends life? Focusing on the positive can give closure. You could share it here or with other friends of hers. Perhaps if there are other friends yoiu could have a remembrance meal at a restaurant. Other people will donate flowers to a church in memory of or put a remembrance in the local paper.