We have a number of Sonos speakers, three of which use Google voice search. We each have our own Spotify user profiles and Google Assistant accounts, including my wife. For both of us, Google complies with commands to do things like switch on lights, and if we ask it "Who am I," it knows each of us by name. But for me, it only functions when I request music. It indicates that it doesn't understand for my wife. Using her Spotify app, she can effectively send music to Sonos, but voice commands are ineffective.
Best answer by Corry PView original
Welcome to the Sonos Community!
Please ensure that both Spotify accounts have been added to Sonos, and that your wife’s Spotify account has been added in her Google Assistant’s settings (via the Google Assistant or Google Home apps).
I hope this helps.