Tvangesti
All they need to do, is go to the desktop on the monitor, right click somewhere on it, properties, display settings and then, in that window, there will be a drop down list, the projector should be on that list, select the projector as the primary display.
Yup, yup. Good call.
Defautedly, when a second "monitor" is set up under Windows, a "spanned desktop" is created. The icons reside on the first desktop, and the second desktop allows for a space to drag application windows. If your mom is trying to run a powerpoint application, all she has to do is drag the powerpoint window off of the right side of her screen and it should appear on the projector.
I honestly wouldn't recommend setting up the projector for use as your primary display, because your mom likely won't remember to switch it back every time, and when she disconnects, the laptop won't show a display.
Instead, there should be an applet in the control panel. It'll be titled ATI or Nvida control panel. Inside, she can set up the second monitor as a cloned desktop instead of a spanned desktop. If she sets it up as a cloned desktop, she can disconnect and still get an image on her laptop screen afterward.