Hi there. Well, for some kids, they do not naturally develop strong social skills and their parents and caregivers have to teach them to help them along.
She sounds a little immature for 8 but then again, as the mother of an 8 year old, they are still young and there is a wide range of 'normal' behavior. I do think though that you could help direct her with things like personal space.
As her aunt, it would be good to know if her mom feels as you do. That is the starting point. Have a heart to heart with mom with no judgement but just care and concern. And try to have some suggestions for her.
Here is an idea for personal space illustration. Get a hoola hoop and have her put it around herself. Then . . . try to get in with her. She'll laugh as it is obviously too close. so, she must picture that people have hoola hoops around them as their personal space. If she gets too close, it is like trying to get in their hoola hoop. People often call this a bubble as well. Bubbles touch but do not go further or they will pop. Another idea is robot arms. Stick arms out and walk like a robot. Then have her do the same and walk to her -- your arms will bump. We should always be robot arms apart from one another.
Another issue that she may have is reading facial cues. Putting feet on someone may be annoying to that person. How can she tell if they think it is funny or annoying? Help her with this by practicing facial expressions. You can play a game of making them and have her guess what emotion you are pretending to have.
These types of games will help her understand the dynamics of other people for the situation you describe.
As to what she plays, that is tough. Kids are at all levels of imaginative play at that age. I try to incorporate 'main stream' things like what I notice other kids my child's age are into while letting them do what ever comes to their own mind. So they can 'talk the talk' with their peers but still be a horse galloping across the yard. She's 8 and being goofy sometimes is part of that I think. As long as she can then fit in when she wants to as well because she is introduced to things and 'coached', she'll be fine.
good luck