Installing Snow Leopard or Leopard on an early 2009 MacBook
Leopard  (10.5) came out in 2007, Snow Leopard (10.6) was in 2009.  Most of the time when this error occurs, it's because the hardware didn't exist when the installation media was created, so it doesn't know how to install.  Typically, the hardware contains hardware for which the installation media doesn't contain proper drivers.  More importantly, though, Leopard and Snow Leopard are out-of-support.  

The early 2009 MacBooks will support the latest version of OS X, Yosemite (10.10).  To ensure you're running a supported OS, I would install OS X 10.10.  If you or her were to take this laptop into an Apple Store, they can assist with installing Yosemite.