Fixed. Thank you

The correct words for the blanks are (i) diffident, (ii) finesse, and (iii) impact.

Breakdown of the Blanks
- Blank (i): diffident

The sentence describes Eleanor Roosevelt as "tremendously awkward." The word diffident means modest or shy because of a lack of self-confidence. This word fits perfectly with the description of her being awkward and lacking a strong presence.
- Blank (ii): finesse

The second part of the sentence contrasts her initial awkwardness with her later development. She "found her voice, and with it, social..." The word finesse means intricate and refined delicacy or skill. Finding her voice gave her the social skill and poise she had previously lacked.
- Blank (iii): impact

The final blank refers to the effect of her three years at the school. It says that the something "of those years...would last a lifetime." The word impact means the powerful effect that something has on a person or a situation. This accurately describes the profound and lasting effect her time with Mademoiselle Souvestre had on her.

The Complete Sentence
"For more than 40 years, Mademoiselle Souvestre was the headmistress of Allenswood, a girls' school outside of London. Among her most famous pupils was the young American Eleanor Roosevelt, who became a distinguished U.S. First Lady but who was then a tremendously awkward and diffident girl. An orphan, Eleanor was raised by relatives in New York, but it was under Mademoiselle Souvestre's tutelage in England that Eleanor found her voice, and with it, social finesse. Although Eleanor spent just three years at Allenswood, the impact of those years with Mademoiselle Souvestre would last a lifetime."