Ivy was one of the many "Gossip Girl" characters that joined during the show’s later seasons but immediately made up for lost time by raising hell on the Upper East Side.

Though Kaylee DeFer’s character initially claimed to be Serena’s cousin Charlie Rhodes, we later found out that Ivy was an actress who Serena’s aunt hired to play her daughter.

You would think this revelation would be the end of the Ivy saga, but unfortunately, she continued to wreak havoc by dating Serena’s on-again, off-again boyfriend Dan and his dad Rufus and also Serena’s dad William, publishing all of this and more in the autobiography she wrote at the end of the series.

https://tvline.com/lists/worst-tv-characters-cast-additions-the-office-buffy-gilmore-girls/worst-tv-characters-late-additions-ivy-dickens-gossip-girl/