This is not a friendship - this is a needy, demanding, self centred lonely person preying on your good nature. That siad of course you too need a friend and maybe she fills a little gap, if not very well! Some really good ideas above:
Ring your own doorbell (I'been guilty of that), or just say "oh there's a delivery man coming up the path, better go".
Tell her you will arrange a chat-time date, make a cuppa and put your feet up and gear yourself up for 'listening-time'
Be unavailable, sometimes you are
Find some better quality friends!
I can tell from your message that you are a kind, caring, generous and loving person who wants to do the right thing by your family so don't feel bad about withdrawing a little from those who drain your energy even further, you are not a bad person. From the posts I have read, we are all thinking of you and your dilemma and admiring your strength, courage and commitment.
Desperately sad story of the assisted suicide of a grieving mother

