Read it. Her inbox might have been limited, but a backup existed until that limit. There is no way the backup was limited to internal communications. The only way the selective emails (emails to Obama Administration) to have disappeared off of the IRS server / backup is willful malfeasance.
The committee is asking the wrong questions. The archived storage on the computer was limited to Whitehouse communication only? No way.
I think most IT people would agree with the willful malfeasance and or gross negligence assessment. Trusting employees to print out email certainly wouldn't be my backup plan..