You have mutual friends, that doesn’t mean you need to get her text messages, her facebook posts or her tweets. Block everything and keep the drama out of your life. Set up a ring tone for her that lets you know its her, then you can make a decision in the moment if you want to risk the drama.
There are a number of people in my circle of friends that I do not see on social media.
And if you are truly worried, let her know you are working on weaning yourself from your phone (not necessarily from her) - so if she ever truly does mean it, you are not the person she should text. She should call 911 or a suicide prevention hotline (or a friend who will put up with this shit).
(I’m old - 47 - and my phone is often in my purse or on my desk when I’m not at it. Its taken my fifteen year old son far too long to understand that text is not two way communication when its his mother - if he wants to make sure I’m coming to pick him up - he should actually make sure he’s reached me and I’ve responded).