Blank app screens after update - How do I reinstall iOS 7?

My wife and I have the 4S. We did the iOS 7 upgrade on our phones (and our iPads.) Mine works fine but hers shows blank screens when she opens reminders and calendar. I'm wondering if her download got corrupted, so I'd like to reinstall iOS 7 on her phone again, to try to fix it. How can I do that?