Generally, NO; it's actually illegal for airlines to give passenger information to just anyone. If she's a US national, she will have to provide contact information for somneone not traveling with her. I would suggest of course having her give your contact information. I'm not sure if that would suffice as permision for the airline to disclose anything to you regarding your sister though. If she's not a US national or if the aformentioned is not possible. It would be best for her to inform the airline at the airport she's checking in at that she gives permision for you to receive information regarding your sister. The airline should send a message to JFK explaining this arangement. If that doesn't help, then I don't know. Good Luck!
Generally, NO; it's actually