Why didn't she signal the passing helicopter?
Was her phone on silent?
Did she miss calls from rescue services?
Why didn't she find an unexposed spot?
Why didn't she protect herself from the cold by using available emergency gear like a bivouac sack or rescue blankets?
Should he have stayed with her and died on the mountain? Of course not.
Again: She was an adult. She chose to go on a dangerous adventure. She was responsible for herself.
It's a terrible tragedy, but she, not he, is responsible.
When I was skiing in Switzerland with my son, we decided to ski from one town to another. I son skied ahead of me, and I found myself alone, high in the alps, very tired, and with only a series of steep, triple black diamond slopes on which to descent to the town of my destination. I made it, well after dark. If I had died on the mountain, it would have been my fault. Nobody else's. No one but me would have been to blame.
One of the smartest things I ever learned, I learned as a pre-teen: "It's my own damn fault, nobody else's."
Apparently he told her he was going to get help. She must have trusted him. She might also have become confused because she was hypothermic.