Syncing exchange on ipad

I have a user that has an ipad and has setup exchange to sync using the OWA url. It works fine from her house and other places outside of the office. When she comes into the office, the exchange won't sync on her ipad. I am guessing this is because it is using the OWA URL that is only valid externally. Is this the case? If not, how can I get her ipad to sync to exchange inside the network?

Thanks,

Justin