"Emma's red hair and skin complexion even resembles Rosie's," Elizabeth Koehler-Pentacoff tells PEOPLE

By Liz McNeil and Karen Mizoguchi
Updated March 22, 2016 10:20 PM
Credit: Jon Kopaloff/FilmMagic; Getty

No one was more pleased to learn that Emma Stone was cast as Rose Marie “Rosemary” Kennedy in the forthcoming Letters from Rosemary Kennedy biopic than author Elizabeth Koehler-Pentacoff, who actually knew Kennedy as a young girl.

“[Emma] is the ideal actress!” Koehler-Pentacoff, who wrote the New York Times bestselling book The Missing Kennedy, tells PEOPLE. “Emma’s red hair and skin complexion even resembles Rosie’s. I can’t wait to see Emma’s amazing acting skills as she portrays my dear friend.”

On Monday, it was announced that Stone, 27, signed on to play Kennedy in the biographical drama about the eldest sister of President John F. Kennedy and senators Robert F. Kennedy and Ted Kennedy.

According to Entertainment Weekly, the Nick Yarborough-scripted film will “explore the life and final days of its title character, an intellectually disabled young woman who was subjected to a disastrous lobotomy at age 23 that left her unable to care for herself.”

In 2005, Kennedy died of natural causes at age 86.

“Rosemary was a tremendous catalyst for change throughout the world for people with mental disabilities. If the movie portrays her with honesty and compassion, it may bring dialogue and action with regards to mental illness in society today,” Koehler-Pentacoff says.