Is it just that parents are in some ways invisible to some children? I had a medical procedure recently and my four year old DD was in tears talking about how she was worried about me and is just so empathetic and caring, and I rarely feel that sort of emotional connection with my six year old. On the upside, her feelings aren't hurt as easily as her friend's and she seems happy a majority of the time. Someone can be mean to her at school and it rolls off her back. I could get mad as can be at her, and she barely seems to be affected. This can be a downside too, because it is harder to get through to her in terms of discipline.
Oh, it seems that she can be told a thousand times to close the patio door, not to do this or that, and it just doesn't stick, yet learns concepts and facts so quickly. She just seems like a more complicated child than her younger sibling.
Wow.... this sounds JUST like my DS8 when he was six. (wow). It was so bizarre... he loves to cuddle, always has, but when he was six (and under) he was completely immune to emotional connections. I could cry for some reason and it would go right over his head. Discipline was very hard because everything was like water off a duck to him. Two way conversations were rare. The school insisted he was on the spectrum (fyi, our psychologist said no way to ASD, and diagnosed him with ADHD combined type).
Now he's much different. He has developed a lot of empathy, and he's very sensitive. He's very connected now. We have meaningful conversations regularly, and he's very good at telling me how he feels. He's like a different kid.
My feeling is that it has to do with developmental asymmetry. When he was 6 he was advanced in many areas (visual spatial, math, and a little in reading, for example) but delayed in others (impulse control, receptive language, fine motor, etc, and... emotional connections).
Just keep on offering connections to your daughter, and give it time. With every year they change so much
