She is Moses' girl.

She marries the hero so yeah

Definitely

how does that make Tzipporah one of the heroes? Miriam helps move the plot.

Come on, Miriam's role is way bigger. She has a story arc/backstory (Tzipporah doesn't), and drives the plot in several places. That scene where Miriam clues Moses in to his real identity is the most important plot point in the whole movie.

Seriously, name three ways Tzipporah's presence has any influence over the story or the people in it. Her dad Jethro is on screen for like 5 minutes and even he has more of an impact on Moses than she does.

Marrying the hero doesn't make you a heroine, let alone more of a heroine than someone else. That's crazy talk; it's also sexist. Tzipporah's a heroine because she does heroic things, not because she falls in love with a guy. It's also a really unfair yardstick - I don't care what fanfiction says, Miriam can't have that kind of relationship with her brother.

I think Miriam does more for the plot.