Minnesota is a one party consent state:
A one-party consent state permits individuals to record conversations to which they are a party without informing the other parties that they are doing so. In other words, one-party states allow recording of phone calls or conversations with the consent of only one of the parties to the conversation.
Since she was not a party to this conversation, she has in effect committed a wire-tapping felony. If you can get her to admit she recorded you in front of a witness or on a recording, tell her to not bother objecting or you will inform the authorities. End of story.
When I was a hiring manager we interviewed in one area, talked in another.
I was doing start ups at the time I spent half an hour reviewing the prospects work experience and then turned the Supervisors, for whom they might work on them.
Talked in the talk area, voted and then sent an up or down to HR.
I assume you'll never be able to prove she did this, but you didn't shouldn't hire her.