I usually buy little accessories like that for my daughter from ASOS http://www.asos.com/search/anklet?q=anklet&r=2
It keeps her happy to see me as I don't see her that frequently, and they are relatively inexpensive. Not sure why women find it necessary to wear bracelets around their ankles where hardly anyone will notice them, but it's a good idea for a gift, I can vouch that it will get you in her good books