In Jade Regent, I have a new(ish) player. She has played one other game of Pathfinder under an incompetent DM, so she's still learning the rules. She also plays a lot of RPGs like Skyrim and Fallout, and wants to be the best at sneaking, melee, archery, magic, and skills all at once, since those games allow for that. Her friends have said she's not good at teamwork. Is this situation salvageable, and if so, how do I make her understand the point of a party system?
Try comparing it as different jobs and tasks
You can try comparing classes and their roles as jobs in real life. You call a locksmith when your lock is broken, not a plumber or a lawyer. Of course, you could try in real life to train a wide set of usefull skils, but you probably lack the time and will to do so. As in real life, you generally prefer to focus your studies in a field to become efficient in it.
Should you translate it to game such as Skyrim, show the barbarian as a Companion (fierce warrior), the rogue as a member of the Thieves guild and so on...
Of course, she could be the Dragonborn and master all the skills... If she was lv 90, as in the game. She's only beginning her journey, and will grow more powerful with time. But as she isn't prominent in all fields, she must learn to cooperate with ally who possess complementary skills.