I really think she just does what her family does.

I remember seeing some article saying the number one predictor of a person’s voting habits is their father’s voting habits. And I’m sure there are plenty of people who don’t vote in line with their folks, but we’re talking trends here. Politics for most people is cultural, and people learn culture from their parents.

And in addition to the other suggestions here: think media criticism. Citations Needed is excellent for that. It’s not so in-your-face left that a conservative will reflexively reject it, but once you see what the media covers and what it doesn’t you get into the question of why, and that leads very directly to leftist thinking.