What is the French song featured during fashion show in Sept. 29 episode of Gossip Girl not talking about Ca Plane Pour Moi She says Je suis une fille qui aime les garcons?

The song you're referring to is "Je Suis Une Fille" by Étienne Daho.

While "Ca Plane Pour Moi" is indeed a popular French song, it is not the one used in the episode you mention. "Je Suis Une Fille" is a more fitting choice as its lyrics match the scene in the episode.