I wasn't when the problem occurred.Are you playing the latest 0.7.9.2.1?
I didn't think I read it twice, but I may have done. I did read it again today (with the latest release) and was surprised to find that I could visit Miss Winton again, but that was probably a reset from yesterday's play on the old version. I know I did reread the letter after I couldn't get back to the island just to see if I;d missed something, so that's probably what reset it.Did you perhaps read her letter again? There was a bug that resets the quest if you did that, which means the option to go to Avonmore would disappear until you get the quest again from Miss Winton.
I'll talk to Miss Winton, and then maybe go do some hunting on Avonmore, see how I get on.Yesterday's release fixed this.