This is not all that complicated. If you're busy tell her you're busy and suggest a time you are free. If you aren't busy go see her. Some guys get so worked up in the "power struggle" that they often will only agree to see a girl if it's been suggested by them, not the girl, which will sometimes lead to actually never seeing her again.
I ask, what's more "powerful" flaking on her to retain control on when you meet-up, or meeting up with her, spending more time with her for you to instill more face-to-face attraction and comfort by having not just words on a screen, but voice tonality, body language, kino etc to work in your favour aswell. The more you hang out with her, the more she gets to know you, the more she gets to know you the more likely she is to want to hang out again (unless you're a douche
)If you want to add a little bit of 'power' in your favour over the meet-up then the way of doing this is giving a false time constraint, for example "Sure I can hang out for a while, I'll have to go after 2 hours though 'cause I got work to do/studying to do/trimming my pubes/licking a window/whatever"