She can call the dining reservation line to see if the castmember can add 3 more to her reservations, but it can only be done if there is a table for 6 available.
For the reservations the castmember cannot modify your friend will need to keep checking online to see if a cancellation comes up for the new party size. She can also check for an additional reservation for 3 (or 4) at close to the time of her current reservation. When both parties check in at the restaurant they can request to be seated together. As much as possible the castmember will try to seat everyone together or near each other, but it is only a request and not guaranteed.
She can also subscribe to the dining cancellation thread for her month, but be sure to read the rules in the first post:
http://www.disboards.com/threads/new-cancel-thread-guidelines-june-december-links-here.1802381/