How do I login to an Apple ID if I've forgotten the password and the trusted phone number?

Right so my friend has forgotten her Apple ID password and she's trying to get apps from the App Store, however she can't because that requires the password. As a result of this we tried to change it except we need a certain trusted phone number but we don't know what that number is. We know the email for the account, and she is logged into it on her iPad she just can't get anything. Can anyone help?