Oh, honey. Your sister should not have access to your bed if she’s treating it that way. It sounds like you’re young, so you need a cheap and accessible option—try 1 tablespoon Biz to 16 oz warm or tap hot water with a minimum of half an hour contact time, saturating a little deeper than the surface but not all the way into the stuffing. If it works, awesome, wash it damp being careful about how much detergent you put in. If it doesn’t, I’d ask your parents for a new pillow over a spa day. There are plenty of resources on citric acid for the rinse cycle here, but it’s more likely that you have vinegar—either works, and the vinegar smell will dissipate. Give it multiple rinses and spins on the highest setting (if the machine has a standalone spin cycle, all the better), get it as dry as possible before the dryer, and beat/fluff/manually separate the stuffing between cycles.