Nicely put ALLNEWTAKETWO.
I have 3 steps (adults now). Two I get along fine with and I think it's because fundamentally, I LIKE the people they are. However, the youngest, at 18 (now thank God, at Uni) has been a bloody nightmare for me. I first met her, aged 12. She was wary. Her parents marriage ended, 3 years before DH and I met, because his wife had an affair. Nothing to do with me.
From the off, she was rude, in a way that even at 12, I wouldn't have gotten away with and I certainly pull my own son up (now also a 12 yr old) for much less. However, allowances were made as she was the youngest/the divorce etc. Now, 6 years on, she doesn't want anything to do with me, my son or more importantly.... Her dad. DH tries very hard to keep communication up but sadly for him, it's mostly thrown back at him.
And, I think ALLNEW has it, really...... It's not WHO she is but rather HOW she is. I think she's just not that nice a young woman. And if she were not my husband's "child", I'd have walked away from any kind of relationship, long ago. Of course, this doesn't bode well for "our" future but, I've tried as hard as I'm going to with this young woman.
We recently had visits from step son (22) and oldest step daughter (23) and as always, they were a pleasure. I like them both, very much.