I see it as a shyt test, where you can't win either way.
If you call back, you look like a chump who checks his "missed calls" regularly looking to see if she called.
If you don't call back, she might interpret this as a sign of disinterest or be pissed or whatever.
The way I handle it is to bust them on it in a fun, laidback way:
"Hey HB, I saw you called and didn't leave a
message. You're lucky I saw you called... my phone only shows me the last missed call, so if someone else called after you, I would have never know you even called! Next time, leave a voicemail. I love hearing your little messages anyway."
If she does that shyt again, I call back a day or two later (not the same night) and say something like:
"Hey, did you call me yesterday? You didn't leave a v/m. You know, if you're not trainable, let me know now..." and take it from there.