Creamegg - its about getting the air pressure in your ears to the same level as the air pressure outside. As you go up, the pressure outside decreases, so the ears let air out, which they do quite easily, but they aren't so good at taking air in on the way down.
Apart from the old pinch the nose and blow trick, I've found chewing something (gum, mentos, whatever), Vicks Vapodrops (clears out all the sinuses and makes it much easier to equalize) and, believe it or not, yawning work the best (when you open your mouth really wide the ears will pop if they need to, however this does cause a slight pain). Have also heard that smelling eucalyptus oil helps.
Give her something chewy on the way down would be my advice
