PinkBlush Maternity 💞

I'm trying to order my baby shower dress & so confused, I did my measurements to determine what size & size chart pretty much told me I should order a Large 😐 I've been a xsmall/small pre pregnancy, I'm currently 4'9 & 156pounds. My sister told me just to get a small, she said she went a size up (she's always been a medium) & had to return everything for her original size, I don't understand ,when my sister has way bigger boobs & bigger butt & thighs than me, and we are about the same height, maybe an inch apart. Can anyone give any advice on ordering from here ?