As an experiment and an alternative troubleshooting step, try sending the photo directly from the mail app and not from the photos app.
Start typing and email and then hold down anywhere in the body of the email until a black options bar pops up Select Insert Photo or Video from that options bar. A window will pop up with your photos in it. Choose any photo. Then try to send the email.
If that works, the issue could be in the photos app. Try force closing the photos app, reset the iPad like Carolyn described and the try again from the Photos App.
In order to close apps in iOS 7, you have to drag the app up from the multitasking display. Double tap the home button and you will see apps lined up going left to right across the screen. Swipe to get to the app that you want to close and then swipe "up" on the app preview thumbnail to close it
Reset the iPad by holding down on the sleep and home buttons at the same time for about 10-15 seconds until the Apple Logo appears - ignore the red slider if it appears on the screen - let go of the buttons. Let the iPad start up.