Well...I wrote this with OSR mentality in mind: Experimentation. The noose radiates magic. She appears as a woman with a broken neck. When they walk by the tree, they hear the sounds of a swinging gibbet. The noose is also found right in front of her inner sanctum. So...it isn't going to be easy to make the connection, but I think the clues are there, if a bit subtle.
As far as XP, that's up to you man! You're the GM. Would I give some XP for not really defeating her but keeping her at bay for a year (or however long)...maybe? I've been known to be stingy. lol.
As far as the narration in the beginning, that's again up to you. I figure if they PCs question the people of Ashtonshire, they will learn all of the information. If you want to drop it in front of the players for the purpose of a one-shot, go for it. I do that sometimes just to cut to the chase and get to the action.
If you did a short film, or animation, that would be awesome. I have a fledgling YT Channel that I would love to put it on as a sort of marketing thing. If that is okay with you, of course. DM if you'd like to hashout the details.
Thank you for commenting!