Athena helps Telemachus prepare for meeting Nestor in several ways. First in her first meeting with Telemachus, she helps to give him the confidence and assertiveness to take action against the suitors and to begin a search for his father. Secondly, she does obtain the ship, men, and supplies for him to use while making the suitors sleep. Thirdly, she went with him disguised as Mentor giving him encouragement and advice along the way. When they arrive at Pylos, Telemachus did not want to leave the ship, and Athena, as Mentor, gives him advice and nearly has to push him off the ship to overcome his diffidence in approaching Nestor.
I think he needs to see Mentor not only because he one of the last to see Odysseus alive, but also because Athena knows the experience of the search and of questioning Nestor as well as hearing his answers will help Telemachus grow and achieve manhood.
Telemachus must meet with Nestor to find out what happened to Odysseus.
Athena helps him by disguising herself as him, and casting spell over the suitors to make them sleep, and procuring a ship and supplies.