There IS a difference between Lease with Option to Buy and Owner Financing:
Lease-to-Own, or Lease with the Option to Buy can work a variety of ways, but basically you lease the property from the owner. You typically pay a higher rate of rent than you normally would for the same house because a portion of your payment is going towards a down payment on the house. You are also normally asked to pay a larger deposit. Often with Lease-to-Own it's non-refundable. In addition to the lease, you also sign an "Option" contract. It basically states that you have the option to purchase that house for a set, pre-determined price, within a set number of months or years. If you don't exercise your option, then at the end all of the money normally ends up with the landlord/owner.
Owner Financing is where you purchase the house, but instead of obtaining a loan from an outside source, the owner of the home "carries" the note for you. Typically you'll pay a much higher rate of interest, and typically the purchase price of the house will be higher than if you were to just buy it outright. Most owners require a sizeable down payment. If at any time you default on the payments they can foreclose on you and regain ownership of the house. Then they'll start the process all over again.
So, I'm wondering why you are paying the tax bill if it's owner financing and why she would have a say over your improvements at all?