My sons, both ADHD do the same thing. But my older son, now 8, is the big hugger. He wants to hug his friends, teachers, everybody. The thing with true ADHD is that they constantly have a need for attention. Regardless of how much attention you, it will not be enough. They thrive on this. If you don't say you did good today or something like that, they will seek it out. If I say to my younger son, wow that's nice or your being good today, then my older son pipes up with what about me mom, am I being good, etc. They both hug their teachers at school. I can't say there is anything you can do about it. I haven't found anything to dissuade them fro doing it. It bothers me because I often think other people don't think I give enough attentions to my kids, but it's just the opposite. I can't offer advice other than to say I think its normal in ADHD children.
There was a child in my son's K class who sounds just like your daughter. She was quite the hugger -- boys and girls and parents-- you name it. She did grow out of this stage.
I would not worry about her upsettting anyone at this point-- because if she does something that offends a child, the child will let her know. And I cannot imagine a parent being upset at a sweet little girl hugging their child.
I think discussing with her the importance of appropriate vs. inappropriate affection is really key. It might also make sense, for her case, to try to get her to focus on how people are reacting to her actions. If she tries to hug someone and they make a face or pull away -- she needs to know that its not welcome. Perhaps you could do some role playing with her on both of these aspects so that she can become more aware of how to modify her behavior based on others reactions.
Frankly, I wish my child hugged too much -- hugs not slugs, you know what I mean?