I have been in this relationship for almost 4 years. SO moved in to my home (the one I am still trying to settle with my ExH) after 6 months (facepalm). So when I met SD8, who was then 4, she was pretty much out of control. SO has stepped up a little in parenting dept, but I chose to disengage with her about 2 years ago because she was just too much, and SO needed to step up. 
Long story short, she's a strange kid. I am an SLP so I meet my fair share of funny little personalities. I have never had a problem with forming good rapport with kids. But this kid... I just can't. I've tried, I really have. So I decided to disengage, and I guess it's made life a little easier. But this kid is 8 now, and she acts like she's terrified of me when I talk to her. She literally walks in the door and completely ignores me. She will say goodnight to my BD while I'm reading to her and not say a word to me. I mean that is just rude behaviour, and she's certainly not taught any manners or to be considerate of others by her parents...but have I caused this by disengaging? 

Can you still develop an ok relationship with a child who lives with you 50/50 with disengagement or am I just kidding myself?