So I have a family account, and my wife and I both have logins. Alexa will only use "her" spotify account, which it announces when playing from Spotify, but if she's using Alexa at home, I can't use it in the car or at work. Why don't they work like I would expect? Multiple users, multiple sessions.
We have Alexa and our Spotify accounts work. You or she have to add you to the household whoever has setup Alexa. So if your wife set her up then she needs to add you to the household from within the Alexa app. You will then be able to login to Alexa separately by saying, “Alexa, switch accounts”. Now you should be in your own account on Alexa and from there your Spotify account.