You have made optimistic progress with Ring, as she allows you to rub behind her ears as she eats! Don't give up hope; continue to spend as much time as possible with her.

I used to sit by the cage of my now RB feral, Muskrat, and read nursery rhymes and sing to her. Being completely wild, she of course initially would recoil from my attempts to touch her, so I slowly began to reach out to her via a brush, which she did not mind at all. With much patience, and taking the situation one step at a time, she eventually became fully trusting (of me, exclusively) and would sit on my lap and interact with me just like my tame kitties. It was a very satisfying experience to witness the change in her.

Depending on Ring's personality and pondering the big question mark of what she endured before you came into her life, if you are dedicated and devoted to achieving your goal it sounds like you are well on your way to realizing it.

I believe that your persistance will reap rewards!