Feel free to respond, but put the onus on her to make the plans and then forget about it.
"Sure, just hit me up."
It's hard to say really, just don't bother asking her again should she not hit you up. If she's particularly interested she'll get back to you soonish.
Source: Getting increasingly far-fetched excuses from a girl over a course of a few months. Learning to take the hint is hard!
I responded with exactly that, so cheers.Have the last word, at least. "Sure, let me know" and then drop it and forget it.
To my surprise she actually asked if I was free this coming Friday, but after her lack of enthusiasm I'm not entirely sure if I should even bother? I'll have to see... :/