Usually, in behavioural questions, a candidate is asked about a time that x happened and how they reacted in order, or when they led a project in order to quantify leadership qualities.
Unless the candidate is really unprepared, most people would have read about these sort of questions and come up with some template answers. Now, it's up to the interviewer to ask further questions to get a better understanding but I'm wondering if people approach this in a different way.
As a side note, leadership qualities in my mind have nothing to do with seniority.
If leadership quality is something you wanna test for, you just have to design the questions in that manner - for example ask about how she handled professional failure in the past, ask her to give you some tips to motivate subordinates, to teach you something you dont know, even its a fun fact, like turtles breath through their bottoms.
As for your concern that "most people would have read about these sort of questions and come up with some template answers". You could flush their prepared answers by asking the candidate to give you a 10 second summary of their answer first, then ask them to give another example in a 10 second summary. After they have exhausted their "template answers", ask them to take their time to give you an example other than these 2. Give them ample time. Don't bully them or put them under pressure, work with them to elicit another example and dive deep in a collaborative manner. for example with "why did you think at that time, this was the right approach", "I messed up recently by doing xxx, how do you think I could have handled it better". (Don't do this for all your Behavioral Questions. Pick the last question especially if the candidate is performing well)
End of the day most interviews are a waste of time because 99.4 percent of the time is spent trying to confirm whatever impression the interviewer formed in the first ten seconds. (https://www.researchgate.net/publication/313878823_The_impor...). I cant find the reference for my life, but I think it was Google (or Amazon) that found out that given the same structured interview process, some people were better than others in selecting great teammates that performed well on-the-job. The key is to encourage these type of interviewers to do more interviews.