I would recommend Supreme Commander on the easier difficulties if she wants to get into Real Time Strategies. It's a definitive game for the genre and has a decent learning curve.
For first person shooters, get her into a simple arena shooter. There are plenty of them out there from Quake to Unreal.
As for RPGs, a super simple one to play imho would be any of the Persona games, especially 5 (which I'm going to be talking about for the rest of this). While the game is half school sim and half JRPG. The combat is streamlined to be focusing on enemy weaknesses while balancing strengths and resists on your party. If you like slow paced narrative alongside fun, colorful JRPG styled combat, you'll fall in love with this game like I did. It's got a huge hook, so prepare to spend 60+ hours into a single game. Also, don't worry about the previous games, the story is pretty standalone from the rest of the games.
As for casual games, Stardew Valley is always a personal favorite. Good game to play when in any mood and is perfect for anyone of any skill level.
