Give the whole plant a good wash under a running tap (foliage not compost). I've harvested brassicas from the lottie with whitefly on them (having survived being shaken off at the site and carried home), and they do not appreciate being drowned in cold water. After you have washed the foliage you could put the pot outside for a chilling (tonight looks like being pretty cold) and see what happens. Your mint will come to no harm for getting cold, it's so hardy it can be a b****y nuisance if planted straight into the ground.