"A childhood friend of the player character, who has acted like a little sister to the protagonist for all of their childhood. She is the first character that offers to join the protagonist, near the beginning of the game. Orphaned as a child and raised by Winthrop the innkeeper of Candlekeep, her origins are just as obscure as the player character's. According to BioWare writer Luke Kristjanson, Her character was a late addition to fill a non-psychotic-thief gap in the early levels. We had no recording budget left, so I assembled her lines by editing voice-over left from a scrapped demo. The original character was a guard named Pique. That's why she has no standalone confrontations / interactions with other party members. Canonically, the events of Baldur's Gate are completed with Imoen in the party."
Source: Wikipedia, "List_of_Baldur's_Gate_characters", available under the CC-BY-SA License.