She has played in sand but i'm pretty confident that she didnt eat any, it looked like the inside of the gold glitter gel pens you can get (im certain she hasnt eaten one of them) and it was consistantly gold metallic all the way through (so it werent just spots of it)
It will be something she's eaten without you noticing. Is she at nursery at all?
DD once ate Floam - that modelling clay stuff that has the little polystyrene balls in it. Thankfully I'd seen her do it so the apparent infestation of insect eggs in her nappy wasn't a complete surprise!