How to calm her down about thinking she's pregnant?

ok first off… this is NOT Annonomus… this is a friend of her’s. she is letting me use her name because I need to ask a question so here it goes -

my friend was telling me something about her sister. her sister has been worrying about stuff lately. you see, my friend told me her sister has been wondering if she’s pregnant. I don’t think she is because she’s a virgin. she said the only “sex” she has is when she humps a pillow when she gets bored or something. me and my friend have both told her that she isn’t pregnant but she always says “but what if I am”. she is sort of freaking out since she doesn’t get her peirod monthly. she gets it like every other month or 2 she said and she’s had her period for around 4 years now. me and my friend have told her that that’s normal and she doesn’t have anything to worry about and that she isn’t pregnant. we tried to tell her that you have to have sex with a man and get his sperm to get pregnant but she still goes into “what if” things. so how are me and my friend going to get her to see she’s fine and not pregnant??? because everybody knows you can’t get pregnant from humping a pillow correct? well thank to Annonomus for letting me use her screen name to post this and thanks to anyone who may help out in anyway. oh and if there’s any people who want to say mean things… don’t yell at Annonomus… because like I said THIS ISN’T HER. she’s letting ME use her name… I told her I had an important question to ask and she said ok. so yell at me not my friend Annonomus. thanks.