Since Demacian noble marriages tend to be arranged, I assume Lux's parents have her set up?

And I'm guessing that Lux's betrothed is going to be some asshole noble who she would completely hate, yet he'd only want her to bed her and to make children/heirs. Probably the typical loveless arrangement.

Would she instead choose to follow Fiora's example and refuse the marriage, or would her indoctrination override any of her qualms?

I'd actually love one of those "cliche" scenes where Ezreal breaks into the wedding at the last second and causes it to be called off (somehow). Unless of course everyone hates the Ezreal/Lux pairing.