dd 2 is having a big end of term party tomorrow. The deal is huge tent in the garden, I provide pasta/sauce supper they bring own snacks and entertain themselves. Have done this a couple of times for older dc and all gone well.. The problem I need advice about is as follows. We are a large family, I have 4dc Dh has 4. He has his eow (just the youngest 2 now as folders are late teens and visit/stay when they want). Dd who is having party is 12yrs .Dsd 2 who is with us for the weekend is also 12yrs. Her younger sister Dsd 3 is 8yrs. I have insisted that Dd2 invites Dsd2 to join in. Dd2 is furious. She says she won't know any of her friends, besides 'she is so babyish and uncool' She also points out that Dsd is her step sis and not her mate and they have nothing in common. In dd2 defence I do see they are very different. Dd is a typical 12yr old goes to excellent large state comprehensive, has much older siblings and has matured faster.. Dsd2 goes to single sex small private school and hangs out with her younger sister. Dd is all about boys, make up music, Dsd gets the giggles if a boy who isn't her brother talks to her. Dd wants my DH to take his girls out for evening rather than force her to be at the party. We have been a joined family for 7 yrs and these two get on fine, but will never be close friends. Aibu to say she is your sister invite her !! ?