I had a lot of anxiety (and probably ADHD) growing up and was afraid of eye contact and found myself staring at people's chests instead until I learned people didn't like that. I'm still not great with eye contact (except for intimidating people haha), but I learned to look at their forehead.

Maybe it's something similar with her?

Interrupting and bad eye contact are parts of autism/ADHD. You didn't say how old she is, but just try to teach her some tricks (like looking at someone's forehead instead of chest). I still interrupt people because there's a need to get the thoughts out while I have one that's relevant that's been "grasped." The only way I don't do this is by not talking at all because any time I get a moment to speak my thoughts have made a million leaps and circles and my thought's are totally off topic by then.

Not saying either of these is the case with her, but just what I've experienced and the reasons behind them.