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This is most likely being caused by a single Pandora account being used on multiple devices. Even though you're upgraded to the Family Plan, each listener on your Family plan will need to have their own account. As long as each person on the family plan is on their own account, you can all listen to Pandora at the same time. However, you still won't be allowed to play music from a single Pandora account on multiple devices simultaneously.
Looking at your Family account, I do see that you've sent out an invite to your wife and that it has been accepted, but there has been no activity on her account for the past two weeks.
If she's been listening during this time, then mostly likely she's been using your account and that's why you're receiving the concurrent streaming error.
I recommend that she sign out of the Pandora account that is currently logged into her device and sign back in with her own account. If you listen to Pandora at home on a TV or speaker system, then I would suggest created another Pandora account specific for that device. This way you'll all be able to listen at the same time.
Hope this helps to clarify.
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