Or, you can just tap and hold on one icon until they all start to jiggle. Then you can drag any icon (up to six) into the dock, or out of it. That's probably what she did.
Be careful not to tap the x that appears in the top left corner. That will delete the app.
As Kevin says, you can't delete the native apps. The x won't even appear on them.
I really, really hope it's not restrictions.