What you are experiencing is a bit different than what the OP was seeing. So try this.
Quit the mail app completely and restart the iPad. Go to the home screen first by tapping the home button. Double tap the home button and the task bar will appear with all of your recent/open apps displayed at the bottom. Tap and hold down on any app icon until it begins to wiggle. Tap the minus ➖ sign in the upper left corner of the app that you want to close. Tap the home button or anywhere above the task bar. Restart the iPad.
Restart the iPad by holding down on the sleep button until the red slider appears and then slide to shut off. To power up hold the sleep button until the Apple logo appears and let go of the button.
Or this.
Settings>Mail, Contacts, Calendars>Email Account>Mail>Off. Then restart the iPad, go back to the settings and turn mail back on again.
See If either of this things work.