I don't have any real advice since I've never really experienced this before.. But I think it sounds like you are on the right track. The only thing I can compare it to is how my dog Taggart sometimes wants to play with my cat Leo and because they don't "speak the same language" Leo can have a hard time telling him that he doesn't want to play.. So obviously that's when I step in and tell Taggart to stop it.
They get along pretty well though and most of the time they can play quite nicely with each other and Taggart is getting better and better at understanding "cat"

So yeah..
I would definitely continue to interfere every time Celeste tries to play with Falise and Falise doesn't want to. Hopefully Celeste will learn in time that a growl from Falise means no and she'll find something/someone else to play with.