Hey man you gotta learn to forgive yourself. Again, it seriously wasn't your fault.
I get it, she's been gone for almost 5 years now, but there's nothing anyone of us could have done to stop this sadly.
What happened, happened.
You know what I think you should do? If you haven't done this yet, I think tomorrow, you should buy or find flowers to pick from a garden or something, visit her grave and leave the flowers on her grave.
Maybe even say what you would say to her as if she was right there standing next to you. I know it sounds silly but I think it will help you grieve much easier.