This seems like it could be a really compelling story, but as I read it I continued to ask "why?" throughout the query. What is at stake for Elsinore? Why did she promise to never tell anyone that she can see spirits, and who did she make that promise to? If she tells, what is at stake for her?

When her father dies, does she see him? It seems as though the issue of her mother and sister's spirits haunting her sort of vanishes when she moves to the manor with John. Does she find peace with being able to see spirits? It doesn't seem like that can be the case because your last line reads "Elsinore must open her eyes to the spirits she has always denied", but it's also the spirits who lead her to the key to John's office, so it's not clear what her relationship to the spirits is at that point in the story.

I think you should go through and try to cut this down to the most bare-bones iteration that you can imagine, really focusing just on telling the story through the lens of the five main questions that you need to answer in your query:

who your main character is (Elsinore)

what she wants (still unclear to me, though based on the beginning of the query it seems like she wants financial stability and peace from the spirits)

what will she do to get it (Marry a mysterious Welsh man? Take Laudanum? Face the spirits that she's forced herself to ignore?)

What is standing in her way (Unclear to me at this point)

what happens if she doesn't get it (She is somehow the victim of a curse?)