This seems like a network problem of some kind, so I would continue to focus on what might be different about your wife's computer when compared to yours.
Is she on wi-fi rather than a wired connection? Does her computer have multiple interfaces or complicated network configuration (like a laptop with both a wired, wireless, bluetooth, VPN, etc. connections)? Can you post the Win+R, cmd, ipconfig output from both computers?
Is there any other security software running on her system aside from Windows Defender? Norton, McAfee, any kind of VPN, etc.