I fly out of terminal C fairly regularly at BOS and don't anticipate there being an issue for your granddaughter. Over the summer the central security check point was completed allowing access to all gate areas from a single checkpoint and helped reduce wait times. All of the JetBlue gates are in the same area and their personnel are by and large friendly and willing to assist passengers. If the family would like, they should be able to obtain a gate pass from the ticket counter allowing them to accompany her to the gate area. If you have any other questions, feel free to ask away or PM. Safe travels!