Re: A valid reason? Boundaries
It may sound cliché but you might want to be honest. For strategic reasons.
It'll let her know you aren't waiting around for her while she's playing head games. So she's inclined to open up to you about her feelings and expectations. And she seems the type that would show up unannounced and you don't want to be caught in a lie like that if you see a serious future with her.
Of course there's always just saying you need space.
"All things are subject to interpretation. Whichever interpretation prevails at a given time is a function of power and not truth."