Did Vinnie Ream visit the White House daily for 5 months?

[JMadonna]

In an 1866 letter to Alphonso Dunn, Mary Lincoln called Vinnie Ream "an unknown person." If Vinnie were really at the White House daily for 5 months how could she be unknown to Mary?

I am curious if anyone has ever come across an independent sighting of Vinnie being in the White House. There are many diaries, letters, books, etc. written by folks who knew Lincoln and were at the White House during his administration - did any of them ever corroborate Vinnie's story?

Maybe she was the 19th century's Monica Lewinski.