Wife's Windows 8.1 notebook won't connect to wireless network when my computer is connected at the same time

My wife's Windows 8.1 (Dell Vostro 3450) notebook won't connect to our home network whenever my notebook is connected to it. It works fine whenever mine is not on. My router is a Netgear N600 (WNDR3700) with the latest stock firmware. All other devices (2 iPads and 2 iPhones) are working fine.

It says it "can't connect to the network". Digging on the event viewer I can see an entry under DeviceSetupManager source saying "Metadata staging failed, result={0C845880-00D2-1000-9F61-78ABBBA90644} for container '0x80072EFD'" and lots of DNS queries failling after that entry.

I already tried:

• Assigned static IP based on MAC address both for my notebook and hers
• Switching wireless channels
• Disconnecting(forgetting)/Reconnecting to the network
• Uninstalling/Installing drivers - Tried old and new ones
• Checking the option to prevent Windows from disable the wireless device to save power
• Changed the network name and password

I also looked on the routers log, but couldn't find anything.
Any ideas on what it might be before I start rebuilding the network using OpenWRT or DD-WRT?