It is very interesting that the friend is already showing behaviors usually done by adults, and it is a bit concerning for it to happen at such a young age. This is the usual selfish and manipulative tactics common in adults. Making people choose between me or them, always wants to do things they want, etc. For children, this is a bit ok, and is usually a sign of being a spoiled child. But when they don't outgrow it and continue with this behavior when they get older, that is when it is usually a problem. I usually avoid these people, but I hope your daughter doesn't lose a friend.
It is actually really interesting in this case, as the girl is a ray of sunshine every time I see her, but I also wonder how much of an act it is at times, or what it is a response to.
I'm not sure, but I've seen it in other kids as well. They are so bubbly and friendly too. It might be that the parents are enablers and let them do what they want most of the time. I've seen it on an only child as well. So maybe there are different factors.