Then libertarianism will never be more than an intellectual exercise.
Perhaps so. But the right to self-terminate is one that is recognized in a few nations these days, after judicial review. If you are terminal, and can show a court that you're not simply depressed, there are things that can be done. Regardless, it's a matter of reality that most any adult has self-ownership under the concept of 'right to destroy', because no one is held responsible should you kill yourself. And most everyone has both the chance and resources to do themselves in, and there isn't usually much a law against suicide can do about that.
Under rare circumstances and with a guardian appointed to make sure that you are not being manipulated, I see suicide is a valid option. But the vast majority of suicide attempts are due to temporary issues and it makes sense to me that we stop the person and give them a chance to see the bigger picture. The suicide of a woman who has just given birth will have devastating impact on her family and if the reason for it is postnatal depression, then its well worth restraining/medicating her a few weeks.
I guess I don't think her life is just her own - its also partly her baby's as the baby depends on her. So that means your person is not wholly your own to dispose of as the mood takes you.
EDIT: I still think ownership is the wrong concept here. Hospitals pump out people's stomachs all the time. I only know one person who had this done and she was saved a few times. She never complained about people "owning" here or violating the "ownership" of her stomach. Its just the wrong language to describe helping someone at the time they need it most.