Apply the default policy and delete her from the BES. Then set up BIS. The password settings will still be there (according to your configured policy), but she will have the ability to change them once she is in Default. If she or you want the BB back to default completely, you will have to wipe the device.
I hope she realizes that she will no longer be able to wirelessly sync her calendar, contacts and tasks if she is off BES - but I guess you get what you deserve. I detest whiney users who have no regard for security.