Presidents and First Ladies Trivia

[RJNorton]

The following quote comes from a letter that a future First Lady wrote to the man she would marry. She married him about 5 1/2 months afterwards. This was many, many years before he became president. She was 19 years old when she wrote the letter.

"I think that a gentleman has no business to concern himself about the legs of a lady."

Who wrote this to her future husband?