A leader has these four traits:
1. Vision
2. Context
3. Trust
4. Optimism
Vision is what the leader wants the team to become. In basketball it's likely to be hardworking, unselfish, communicative, etc. It's also a vision set by the head coach with the player leader in agreement so that the coach can work through the leader.
Context is making every choice and every action move the team closer to the vision. More importantly, it's making sure everyone on the team knows that choices and actions are intended to get the team closer to the vision so that they don't seem like random things going right. Leadership is done intentionally.
Trust is a personal characteristic. It involves integrity, day-in day-out work ethic, doing what one promises, and ultimately respect.
Finally, leaders are optimistic. No matter what the situation, "we'll get through it and be better off." No team ever thrived on optimism in the face of obstacle after obstacle better than the 2017-18 Fighting Irish. The coaches steadied the team and kept it focused, but someone had the team saying, "Screw it. We're going to keep winning anyway."
Note that nothing I said above requires a fill-the-room personality. A person with a reserved personality can have vision, context, trust, and optimism just as well as the gregarious person can. Skylar Diggins, Natalie Achonwa, and Kathryn Westbeld are three very different kinds of people, but all three were outstanding leaders.
I don't think there was an outstanding leader between Achonwa as a senior and Westbeld as a senior. Good people for sure. Hard workers. But nobody had the levels of trust and respect those two earned.
I really don't know who it will be in the 2018-19 season, if it's anyone. Sometimes the head coach has to fill a void, but it's always better if the coach can work through a leader.
Similarly, I don't know who it will be when the seniors of this coming season are done, but don't write off Jackie Young just because she is more reserved. She's a very smart, very thoughtful young woman who might thrive when it's her turn to lead.