if you can convince her that snes graphics are awesome you should try Secret of Mana, theres even internet/lan multiplayer emulators if you want.. If you dont want to buy it legit/already own it but misplaced it... or whatever.
Swat4 is pretty amazing, albeit difficult to play 2player coop[best with 3-4 in my opinion, although you can do it with more]... so it might not work unless you can convince some others.
Anno1404 is kinda like simcity with ships and trading.. some spy stuff ect.. its not very warfare based, and you can either play it allied but seperate, or as actually the same "person".. Its fun, and actually very pretty. you need the expansion for multiplayer, anno1404: venice.
You could always try a hack and slash like diablo 2, simpler and a lot easier UI then say, NWN2, if uglier. I would also recommend Din's curse, which while ugly as sin, is really fun and a lot more fast paced and replayable.
Men of War: Assault Squad, is kinda like company of heroes, except better, and is a extremely fun game to play coop, as its about working together to push/hold a line of troops/tanks/artilliary ect...
Sengoku/EU3/Other paradox games: you 'could' play most of the eu3-victoria-ect games as allied countries, which is pretty fun if you like grand strategy, and if sengoku isn't very deep, it allows you to actually play coop by having one person be the clan leader, and the other one of his vassals.. But you can actually be a vassal Daimyo and have your own vassals.. so it doesnt take that much away.. and besides you can be coop right until you stab each other in the back or take clan leader from each other ect if you want to play that way.
Wanderlust: basically a zelda-ish combat[with rpg upgrades] game with upto 4player coop... [not as amazing of a world to explore, and its very very linear] It's not really that great of game, but its a very cheap indie game, and if it has some gameplay issues, i still managed to enjoy playing it coop with my friends.