I feel like they are portraying this advance directive thing all wrong. Yeah, I know this is a Soap and they play loose with the facts. But, an advance directive is not a DNR. I know my father had one and it specifically stated that he didn't want to be kept alive artificially if there was no way he was going to recover or very little chance. I'm paraphrasing. It also mentioned that life-saving measures were allowed within standard medical practices when there was a reasonable chance of survival. I would consider Marlena's case to fall into this category.
An advance directive really does you no good if you don't provide a copy to the person(s) responsible for making those decisions. I know my sister and I both had a copy. The hospitals did not. And, it was still up to us to make those decisions based on his wishes. My sister called me and told me the doctors had suggested we be ready to make those decisions and we both agreed he would be too frail to handle CPR or intubation, but we ended up not having to actually make any decision as he died that evening. Now, my sister could overrule me if there was a disagreement since she was the primary decision-maker.