Real World article(written from a Production point of view)
According to background material used for Star Trek Generations, Madame de La Barre was a French woman that was married to Francoise de Picard in ancient 16th century France.
She and Francoise de Picard were the founders of the Picard family line, and drawings of them are on the first page of the Picard family album. She was a distant ancestor of Starfleet Captain Jean-Luc Picard.
This and the family tree in the album imply that they are the farthest back recorded Picard or La Barre known.
The article containing this information was included in the Picard family album during the filming of Generations. However, the information is non-canon as the article was never seen on-screen.