Buying from an elderly lady who wants to sell before she dies

[Barry Je]

I found a great deal with a unique situation and wanted to get your opinions and ideas on how to proceed.

The owner is very elderly and states that she would like to sell her home, but she wants to live there until she dies.  She's selling it for a good 30% less than what it's worth.  In our market, things are crazy, and foreign investors are buying up houses in this price change.  Keeping it off market would work in my favor.

The house is too large, probably wouldn't work as a rental.  It could be a flip, but I can't afford the holding costs and getting contractors is tough.  We need a house to live in as our rental is expiring so my plan is to make it our home since it's already in pretty good shape.  I don't mind waiting 6 months to a year (I don't intend to sound cruel, sorry).

She is VERY old and doesn't feel like she'll live more than a year.  Statistically, probably true.  How would you guys structure the deal so I can lock in this house at a great price but limit risks?  ie let's say she magically does live to 110 i don't want to be waiting around several years.  

My idea was a purchase and lease-back for 6 months at a time up to 1 year.  Other ideas?

Thank you all!