Plug her iPhone into iTunes and on the Photos tab, un-check the "Sync Photos from" box, then goto the Summary tab and check the "Sync only checked songs and videos", then re-sync her iPhone.
The rule is, if it is checked it will be loaded onto the iDevice, if it is NOT checked it will be removed from the iDevice. This applies to most everything in iTunes, music, photos, movies, TVshows and books.
Also, if you have 2 or more iDevices, make sure that they all have a different name, you can rename them in the left hand column in iTunes under "Devices", click on the current name and change it to something like Johns iPhone, or Amys iPhone, That way she and you can have totally different things on each iPhone without messing with each others settings.