If she's that kind of crazy, Commandos 1 & 2 are great time-sinks (the third one just makes you weep if you've played the earlier ones, IMO). I've heard some people say the games are too complicated, though, mostly about the interface. It's kind of like a violent puzzle game in real time and is full of inevitable "you dun goof'd" moments.

I commend you for planning on getting her HoMM3, it shows you're a man (or woman) of honor.

Two Worlds. Casual enough to be played for hours and hours.

I second these three.

Bought this game based on this comment, lol.

Blocksum. It's freeware and very small, so there's no reason not to include it if you think she would like it. It's not a huge time sink on its own, but it's excellent for filling a little time here and there when she can't or doesn't want to spend several hours on something.

It's a brickwell game about single-digit arithmetic. Yes, I'm serious. Blocksum rocks hard.

Depths of Peril and Din's Curse, if she has a thing for Diablo and political blackmailing (former) or Diablo with choices&consequences. Plus, if she's using a laptop, these two games will be perfect.

Well, the enemies do not re-spawn, so it's not like you can play it forever, but I did spend about 70 to 80 hours on it. If you just concentrate on main quest, it will be a bit less than that. Also, it is not like you gets about a hundred of quests like Sacred, for example. But if you just wander around killing monsters, that will take hours.

She would like bloodrayne 1.. I thought it was cool. =)

Edit: or longest journey. one of the best adventures I have played. Still life. That was hard. Did not even finish. Too much wrong kind of puzzles. Liked it still. Maybe I'll have another try someday. And Broken sword. One word. Awesome.

Weird editing but that happens.