A visit to Uxbridge magistrates' court may well introduce you to the sight of mules caught at Heathrow. As a category, they seem to be those mules who are carrying the drugs internally, in condoms and so forth, they are young, and detected by immigration and customs officers because their travel records suggest drug dealing; they have, for example, got several trips to places where drugs are supplied or, typically, they have an unusual route from, say, Ghana to Colombia and then London.
Not often you see one in the category of the women in this case, with such a quantity. But their movements probably gave rise to suspicion, confirmed by any explanation for those movements. Two youngsters, working in night clubs, turn up on a whim in Peru, for a short time, without any evident wealth or means of support ?