About a week ago, I noticed a small lump on the top of my DD's foot, just below the ankle. It's hard to see unless she stretches her foot out, and then becomes almost white as the skin is stretched across it (colourless otherwise, or maybe a tiny hint of bluish colour). It's small, maybe 5 mm or so. It's not a bite and she hasn't injured it. Has anyone any idea what it could be?? She is 8, by the way.