Hi C.,
We're also an adoptive family, my DS is 4.5 and came home from Korea at right around 6 months...so I understand your concern and scrutiny. I'm certainly not an attachment expert, but I think it sounds like your daughter is simply confident and social. My son has always been the type to need to warm up to social situations, so I can't speak first hand. But We have some very close friends whose kids are both bio children and both are very social kids - their daughter extremely so, but their son as well. I'm trying to remember exact ages (the kids are 11 and 8 now), but I'm fairly certain their son was maybe in the 2-3 range when he slept over at our house for the first time, with no issues whatsoever - like surprisingly so. I remember their daughter around 4 or 5 at a fireworks display seeing kids about 150 feet away and asking if she could go see if they wanted to play - that's something my son would never do unless he saw one of his buddies from daycare, and even then he'd want me to walk over there with him. So I guess what I'm getting at is that each kid is different and some are just more confident and outgoing than others and that I wouldn't see it as an attachment issue, especially since she comes to you for comfort - that to me is a big factor. I'm also recalling that around that age my son was a lot more active and less cuddly - testing out the world and not yet afraid of anything. Over the past year or so he's become more clingy and cuddly, and more afraid of "scary" things...so I'm thinking her age and cognitive stage may be playing into it as well.
However, if you're really concerned about attachment you could always get in touch with your adoption agency to find an attachment professional to help you assess the situation and perhaps ease your mind.
Cheers!
K.