yes the extra IP can work, but costs $$$.
when she's not playing the game, access the router configuration
(typical url is something like 192.168.x.y and you'll need to play with
x=0,1,2
y=0,1,2)
verify DHCP is enable for IP & DNS addresses
save/apply the settings
update your network settings on the NIC to also use IP & DNS addresses
Both systems should be able to run at the same time :-0