Sounds like a gradual process. Keep it up, it'll be nicer on her knees, too.

Differences in preferred cadence are not uncommon. If I want to take a higher load share, I stay in a higher cadence, as my gf doesn't push as much then. If I'm lazy, I'll drop the cadence and I will feel her rocket power more

Often the captain cranks are a bit longer than the stoker's. This is to ease with cadence differences (longer cranks->larger circle->faster foot movement->more speed, less torque than on the shorter rear ones). Our Cannondale came with that configuration from the beginning.