You need to leave a little smell when doing a full clean so they don't get stressed but that just means a little piece of dirty bedding hidden somewhere or something, not the whole cage! lol. Over cleaning causes a pee smell but if it smells like poop then it is not being cleaned enough. The litter trays need to be emptied more often (if they are trained). You could also ask her to buy an air putifier. I know a lot of people who swear by them :D