I have this head canon thing from the first episode when Ruby is listening to music in the dust store. The song is sung by Casey (Naturally enough) who also sang as Weiss in her trailer, so to me Ruby was listening to Weiss singing before they met. The songs of the soundtrack are Weiss’ own songs written as a way to deal with the internal emotions that she can’t  deal with or express due to the damage done to her self esteem in childhood. So for instance she sings of Jaune and Pyrrha, Ren and Nora, Ruby and Summer because she can’t express herself in person. It’s a coping mechanism

In my version of their reunion Weiss, no longer being the Heiress, down on her luck, eeks out a living singing on stage in a Mistral coffee house populated with people dressed like CFVY’s fans. Ruby, also in Mistral walking around taking in the sights, hears a familiar angelic voice and wanders in. Weiss is on stage, cheap stage lights and dim houselights keeping her from seeing the crowd. Her voice is powerful, passionate, and her eyes remain closed as she drifts through her lyrics remembering better days.

Finally, at the end of the set, she gets to Mirror, Mirror Part II where she divulges the past she’s hidden from her teammates, the embarrassment, the pain. As she hits the final notes ( I’ll tell you something, I think I might change it all), the stage lights dim and the house lights brighten and she opens her eyes to find Ruby sitting front and center, tears running off her cheeks and a sad smile, clapping softly.

“Ruby!”, she breathes... tears welling in her own eyes.