2 iPhones on an Airport Extreme Problem

I've had an iPhone 3Gs for years and run the internet in our home through an Airport Extreme. My girlfriend and I recently upgraded both to iPhone 4Gs's. She previously had some Nokia garbage. She has a PC and I have an iMac. Her iTunes account on her computer is set up with her Apple ID as it is on her phone. Her email is set up on the phone using the same email associated with her iTunes account. However when she goes to the app store to update her apps it prompts for a password displaying my apple ID and asking for my password. How do I fix this so it is linked to her account? It makes no sense. Every account/password set up on her phone is set to her email address. It's just when you update her apps my email and apple ID come up.