Gmail integration is full. Emails are delivered instantly just like on her BB, you have full search and label functions ect. All Google apps implement quite nicely into Android phones as you probably assume.
She'll get a more expansive phone system, the email will be just as fast with better internal search & label access, and the data plan is cheaper.
When she sets up the phone, she will "link" her main Gmail account to the phone. You can of coarse have multiple accounts, but this one will be what you marketplace apps are linked to ect. All contacts are synced automatically into the Gmail cloud, so you don't ever have to worry about that either. iPhone doesn't get push Gmail (polling interval only), nor full integration of all Google apps.