When you particular things on an account (e.g. redownloading past purchases) you can associate an account to that device (and similarly on a computer) for 90 days (presumably it's an attempt to try and stop people logging into their accounts on other peoples devices/computers and sharing content) : View and remove your associated devices in iTunes - Apple Support
The message means that she won't be able to do any of those things on a different account for 90 days.