first...get access to her car and remove the break pedal shoe, tape a few stink bombs to the metal part and put the shoe back on (so when she hits the breaks, they break) plug up a sink somewhere that doesn't get noticed very easily (like if the parents have a bathroom in their room and they're gone and no one uses it) and turn on the water to a slow trickle. put two raw eggs in a bowl and slide it underneathe the parents bed...won't cause damage but it'll stink like a mother fucker in a few days. go to a pet store and buy a dozen feeder mice (have both males and females) and let them loose in the house. if they have laminated or tile floors (not ceramic) poor honey or syrup all over it and smear it in. won't cause any damage, but sure as hell will be a pain in the ass to clean. that's about all the ideas i got i'm not too good on not causing damage....but if you ever wanna cause damage lemme know, i could give you 1000 or more ways to cause damage, all the way from busting out a window, to making them replace most or all of their engine by pooring sugar in it.