4. Offer Some Unexpected Sponsorships
I know it must this must suck for Taeyeon, but she has to be the one to initiate the truce between her and Jessica regardless of who started their feud. Not only to rekindle their friendship, but because she's the leader. As the leader of SNSD she has to be the one who initiates peace and bring a sense of calm and order within the group, to hold them together and keep them focus. Not favoritism and other shenanigans. She has to lead by example and must try not to wear her emotions too strongly on her sleeves. I know people may hate Leeteuk, but you gotta admit that dude knows how to lead his group. Every member follows his lead (even Heecheul) and lean on him heavily when they need too. Taeyeon has to do this.