I think she'll relish telling Mel what she knows once she realizes that people are coming from slightly different points of time/even different versions of themselves. Learning that about Jon will shock her way more, so she'll be fascinated with Mel's differences.

"Did you know the version of you I knew did this???. Do you know what you told me? Do you know what I did because of it??"

Mel is like the Hound, Arya can't quite decide what to do with her feelings about them anymore.