Don't respond. If it were important, she would have left you a message and/or called again, or texted or emailed you. To return a "Missed Call" just makes it look like you're hanging on like a puppy dog waiting for her to call.

M57 W 57; D30 D28 S24 S20 GD7 GD2 GD1 GD5m GD1m
BD 5/07; W's affair 5/07-8/07

At the end of every hard-earned day, people gotta find some reason to believe. (Bruce Springsteen)