I don't know about thinking about "keeping it non confrontational". that's one way of doing it, and waiting to see if you will HAVE to become firmer.
or, you get on, and right away you change up the way things are, between you two. you ask for a big forward, and if she reacts sluggishly, you get right in there with a pop of the reins or crop. I mean, you make your very first interaction be all new. so , it may surprise her, and really change up her mind, before she has time to start thinking about resistance.
years ago I rode a lazy warmblood, and you'd get on at the mounting block, and then it would take two or three times of putting a leg on and he'd amble off. I took a lesson with a local dressage clinician, and she got on him, asked once with a polite ankle on him, and then took the dressage whip and whacked him hard, three times, really fast ; whap! whap! whap!. man, he jumped out of his skin, which she shut down, and then she asked him soft again, and he moved right off! you betcha!
she said, think of it this way, "There's a new captain on board. this is your captain speaking!"