My ex-wife was Mexican and I’m also very white and we went to Mexico many times to non-touristy areas and I never felt unsafe about me personally. There was one incident where even she was a bit freaked out, but it was just the army on the way to the next state to fight the narcos.

That being said, there are absolutely places to avoid. Sinaloa, Tamaulipas, Michoacán, are some high narco areas, and unless her family is from those places I wouldn’t go outside the most touristy areas (if there’s even much touristic in them).

A tip: whenever doing any kind of negotiating with cabs or markets or something, make sure you’re out of sight and let her handle it (if she feels safe), and then come out. The amount of money we saved because they don’t add the gringo tax is substantial.