SOLVED. Literary, girl committed to insane asylum for trying on her mother's negligee, committed for over 60 years, sister steals her baby, the end is stunning. [s]

[Tamara A Ogorzaly]

It's all in topic. More details: the story starts in India, trauma, family moves back to Scotland, very strict, very cold, set in late 1800s early 1900s, excellent writing.
Begins when great-niece receives information on a great-aunt she did not know existed.

[Lobstergirl, au gratin]

Tamara, as you saw in the popup box when you posted your comment, please tell us around what year you read the book. This makes your query a lot easier to solve.

[Emma]

The vanishing act of Esme Lennox by Maggie Ofarrell

[El]

The Vanishing Act of Esme Lennox for Emma's click

[Tamara A Ogorzaly]

El wrote: "The Vanishing Act of Esme Lennox for Emma's click"

Emma wrote: "The vanishing act of Esme Lennox by Maggie Ofarrell"

Lobstergirl wrote: "Tamara, as you saw in the popup box when you posted your comment, please tell us around what year you read the book. This makes your query a lot easier to solve."

Thank you so much! Yes, that is the title and author...one of the best books I've ever read!