Good management / building games for GF?

Cities Skylines
Factorio
Stardew Valley
Gnomoria

The Hercules games are pretty good time managing games if you want to relax.
And for the rest.. you should really check out good old Zoo Tycon! :)
The original CD must be lying somewhere around...

Sim City 4
One of the Tropico games

how about this: http://store.steampowered.com/app/255710/

Rollercoaster Tycoon 3
Smooth Operators
Unholy Heights
The Movies (If you can get your hands on a copy of that... doesn't matter how ;D)
Cities: Skylines
SimCity 4
Tropico 4 or Tropico 3. Tropico 5 was a massive downgrade and really simplified.

EDIT: Oh, oh! Planet Coaster!!!!
EDIT 2: Damn, the question was so good and I'm on a massive energy rush, so join my WL, since your luck has been shoddy! :P

Stardew Valley

My vote goes to Cities: Skylines too, my gf loves it! Especially after the disappointment of SimCity

Theme Hospital!

Tropico 4/5, I liked those.

Stardew Valley was already mentioned, so I'll add Banished to the list.

OpenTTD

city skyline

Pretty good suggestions

I've also seen Lethis Path of Progress, that looks good

Banished

The Age of Empires series?
Hmm, might have to go replay them a bit to see how much of their draw is due to nostalgia...

Dota 2. You'll build anger and hatred in no time.

....oh wait, wrong one. >_>

If she gets into those games, you can broaden her horizons with Civilization (4 is IMO the best in the series, but 5 will be easier to get into), followed by the old Total War Medieval; if you auto-fight all the batttles, it's a great empire management game. And hey, she may even try a battle or two, which could then get her interested in RTS games.