D..
I'm so glad you wrote again about this. I remembered once you reminded us of this.
I'm glad you had a family member intervene. (Better than a lawyer, especially since the sister offered...)
I was given an original piece of art from a friend who actually put my name on it, as a gift to me. I would be really upset if someone borrowed it and it took me 7 years to get it back. My friend is alive, but still...
I hope that you consider getting this piece of art insured. I'd also take it down if you have a fire in the fireplace... (you don't want heat from the fire to eventually damage the paint...)