My guess would be that your wife’s phone has not yet been connected to the new Wi-Fi. Or, possibly, that you’ve set up a mesh network, and her phone is connected to a different subnet (think extender) than yours and the Sonos is. 

Anytime you change a router, you should always power down every device, and then bring it back up, to flush out any old information each device might be hanging on to, as well. 

Problem solved. 

I powered off the old router / network, problem immediately solved.

Thanks for the help.