Liz - if her parents won't leave you two alone together do it in front of them, it may take a little bit more courage but then you get all three of them together so you can explain what you really meant. You're not a wimp hunny, thats a tough situation to be in. Stand your ground though ok, she does need you!
Im so sorry about your cousin and her

kids ( im not sure if it was a girl or boy) but im sure with a great cousin like you everyone will make it through the tough times together. You just gotta be the stong one. Best of luck and pm me if you wanna talk, i'm here for ya ~melissa