What's the Name of That Book??? discussion

The protagonist is a young woman that had grown up in a tomboyish way w versus her more graceful/noble older sister whom is engaged to a paranoid and arrogant crown prince. The older sister’s knowledge of herbs leads her to create a twist towards the ending with the crown prince. There was a banquet and the older sister poisoned the food to kill the prince. She put the cure in the well water knowing the prince would never drink from there. The suspicion for the prince's death was placed on the protagonist so she was sent home from the castle for her own safety. They also thought she was a witch. I think the protagonist’s love interest is named Simon? Simon was coronated at the end of the book to be the king. They had known each when they were younger. He wore a purple outfit for the coronation ball and someone wrote to the protagonist that another girl tired to win his affections by dancing and deliberately complementing his attire by wearing a yellow dress. Simon doesn’t write to the protagonist after she was sent home but after everything is settled in the castle he visits her in her hometown at the local tavern and asks her to be his queen.

I feel like it’s a coming of age book/YA genre. It’s a standalone.

There seems to be wraith characters that are in slavery that the protagonist doesn’t like how they’re being treated. There's also some Fae folklore and a Fae Queen tomb under the castle that the protagonist stumbles upon. Knowledge of their supernatural history had been suppressed but the protagonist was finding the truth.

Summers at Castle Auburn by Sharon Shinn has some similarities from what I recall.

Yass ! It is. Thank you! I know I had some details mixed up but it was a long time ago that I’ve read it.

Berecca wrote: "Yass ! It is. Thank you! I know I had some details mixed up but it was a long time ago that I’ve read it."

You're welcome! To be honest you remembered waaaaaay more details about the story than I did, some of the ones that you described just seemed familiar enough to make me think it could fit.