When Corvo first encounters her, Miss White is having a conversation with another guest, Ramsey, who is irritated by Corvo's interruption and leaves. Miss White takes no issue with Corvo's company, claiming she "like[s] a man with poor judgement" in regard to his mask, and asks him to get her a drink. If Corvo complies, she will reveal what color two of the Boyle sisters are wearing, revealing the third by process of elimination. This information can be combined with clues provided by Lord Brisby or a letter upstairs to determine the identity of the true Lady Boyle.
Miss White seems to have a prior relationship with Ramsey, likely of a romantic or sexual nature based on his remarks.
Miss White is able to access the second floor of the Boyle Mansion. She seems to be the only guest able to do this. This may explain her knowledge of the Boyle sisters' costumes.
A party guest near the Boyle Party Guest Ledger will tell Corvo to go talk with Miss White if prompted, calling her "lonely".
If the Heart is pointed at Miss White, it will state generic Upper Class Female lines.
On the right, concept art of Miss White.
Miss White concept render.
Closeup render of Miss White.
Miss White with her drink.
Miss White having a smoke.
Miss White and Ramsey have a conversation.
Miss White and Ramsey.
Miss White on the second floor of the Boyle Mansion.