I think that it is important to have the right to make an informed decision and if it is your choice to die, then provided you are of 'sound mind', that must be (and is) respected.
However, that woman has learning difficulties so severe that it is felt that she lacks the ability to make such a decision and truly understand the consequences of her choice.
When someone cannot truly understand the consequences of their choices then to allow them to make decisions that are harmful to them is irresponsible.
My grandma had dementia. If she didn't want to eat, ever, we could have said fine, it's your choice, you know you will die don't you? And let her. Or we could have said look, she doesn't understand what will happen, we have to act. And tube fed her. Which would you have done?
My sons have autism. They want to run out into the road. I say to them no, if you do that you may get run over and killed. They still want to run into the road. Do I let them?
I think when the person, for whatever reason, cannot make a choice understanding what it is they are doing - as it is reported is the case with that woman*, then imo, there is only one option.
*If it is not the case, then I withdraw my argument as it is based on my understanding that the woman does not have capacity.