I don't know if it's because it's late at night, but I'm feeling uncomfortable about your account of your mother. I can't help feeling there may be more to her than you're seeing.
eg she didn't want anyone to know she had tried an overdose, was 'furious' than an ambulance has called. That doesn't suggest someone who wants to be the centre of attention.
I also wonder if you are appreciating how truly terrified she may be about the future, as well as poleaxed with grief at the rejection she has to absorb. She may not have contacted you much in the past because of your view of her - which, incidentally, seems to have popped out when you showed your exasperation that she hadn't started sorting out paying the bills herself.
I'm sorry if that sounds unsupportive, but you do seem to view her very negatively. Have you considered that she might be terrified? I mean, really terrified, beside herself? This isn't your responsibility, particularly as you have your own family and pg to deal with. But your posts seem to lack a basic compassion. I'm sorry if I've got that wrong.
You say she is 'dependent' - that could be for a number of reasons. What comes across to me is someone who is terrified. it was cruel of her husband to sit with her and watch telly as though nothing had changed - no wonder she couldn't help hoping; she is, anyway, very probably battling to absorb what is happening right under her nose. It may not be easy to accept that some people really are 'weak', have little strength, to face what life can throw at them. There could be many reasons for this.
She has no-one in her life. There could be many reasons for this. She is facing an agonising crisis - weak or not, having one's husband leave for someone else is an agonising crisis.
Have a heart, she needs support now. You don't have to be the one to step in and carry all her weight, but perhaps allow her the dignity to be suffering terribly at the moment. It's not your, or anyone's, job to save her. Is it possible that she may have been trying to get that message through to you for some time?