There are a couple of things you can try. The quickest way is to click a blank space on your desktop, hold down the Control key, and scroll your mouse wheel up of down (larger and smaller respectivley).

Note: That same trick works for text sizes, etc. in most programs, and does so just for that program. If you just wanted to make her browser pages easier to read, you can try that while holding the cursor over a Firefox page.

You can also try right-clicking an empty space on the desktop, and hovering over "View", then clicking on a size of your preference.

If none of that helps, let us know.