Presumably there is a short cut icon on your mum's desktop which she clicks on when she connects?
1.RIGHT click and hold on this.
2. Drag it over to the Start button. Don't let go, just hover over the button for a couple seconds. The Start menu should open.
3. Now, (still holding the mouse button down), move up to the Programs menu. The Programs menu should open.
4. Finally, move your mouse to the Startup folder (it should be underlined). Again, point to it for a second and it should open up. Drop the shortcut into it and you're all set. Make sure you drop the shortcut into the Startup Menu and NOT into the Programs menu by accident.