This isn't so much about Anorexia, as the woman being found to 'lack capacity', using the Mental Capacity Act. This is applied to all service users when deciding treatment or planning for care.
The woman had a living will that stated that she wanted to be revived and kept alive, so that stands whilst she is unable to over rule that, as it should.
"Why cant this woman starve herself if she wishes"
Using the format of the MCA, it has been established that she is unable to state her wishes, given her MH state, taken into account of her living will, they have decided that the ethical thing to do is to treat her.
Families cannot be given that power, if the person has a living will.
This is applied toall treatments,as you can temporarily lack capacity as a reaction to perscribed drugs/trauma/or your illness.