I think you could tell her that if she wants to be a landlord then she's a landlord and she can't store things on the property. I think if I were you I'd just lay down firm boundaries. I pay rent and it includes the garage and full use of the property and she is not allowed to store things there. I also think if I were in your shoes that I'd tell her I'm looking to move since she won't sell as previously promised. The fact is she probably will never sell it to you. Better to cut your losses and find a home that can truly be yours. Guess it's just a lesson of have things in writing, even with family, unless you're willing to risk getting burned.