Hi, just read this thread and I would be annoyed too, but I don't think you should get stressed out or annoyed about it... I defo think that you should try and say hello to her, start making conversation. See how that goes, but at the same time you don't want her to start hanging around more... The other option is to just completely ignore her. Don't say hi. Don't acknowledge her etc... I don't think by anyway you should be rude or nasty to her... The way you have seen her dad coming out might suggest he's wondering what she's doing, but he probably won't think it's his daughters doing, and in this day and age you don't want to take any chances, yes it's sad to have to think like that, but unfortunately this is what we live in now. She is only 10... Not 19... So chances are she's maybe just been lonley, and he's been friendly towards her, and she's hoping he speaks to her, or gives her attention again.
Quite sad that the parents dont spend any time doing things with her, yes she could be in playing video games and that could be worse... But kids need stimulated and entertained. And if she does have a medical condition then she should be getting support she needs, not left out to play hoping it changes...