pressuring her wont work, but giving her leniency definitely wont work.
tell her to take her time and she likely will, tell her you arnt upset about tardiness and she will do it more.
all this "im happy to wait as long as you need!" like no shut the fuck up, you dont wanna wait, stop acting like its all fine and dandy
i say best option is say youll be looking for it when she says she will do something, and if it doesnt come express how sad you are that you waited up all night and had to go to bed empty handed. basically guilt trip her when she does this rug pull shit, and only give praise when she keeps to her schedule or gives more than normal