If the version of XP that's installed on the computer has not been properly registered, with a valid product key, then she will get warnings to this effect. After a while, she will also start to experience reduced functionality.
The only solution is to purchase a valid copy of XP. Provided it's the same version as that installed on the computer, then the product key that comes with the bought copy can be used to validate the installation, so a full reinstall may not be necessary.
I understand that copies of XP are becoming more difficult to find.