How to explain to prospective job interviewer why terminated from last job???

I was recently terminated from job at LTC facility, I feel the reasoning was personality conflict with me and New DON (her first DON job), she nitpicked to find reasons and I was never "wrote up" for anything in the 2 years I worked there. I took the blame for an RN taking home a bottle of Roxanol and went on vacation while this med was in her pocket at home, just as an example. She also terminated another RN the same day and took 3 aides off the new schedule without ever speaking to them.
Just 3 days after this has occurred I have an interview scheduled for tomorrow. How do I explain why I was "let go" without downgrading the facility and the DON????
Any and all advise will be appreciated! By the way I am interviewing in a clinic in a small community.
Thanks!