Ummmm....... I don’t even know wHat to say to that.  It don’t leave her alone in a room with your baby

I wouldn't put too much heart in the video game bit. 

When I was a kid in the PlayStation 2 era we'd play The Sims and light the house on fire . We played mortal Kombat, grand theft auto basically things we shouldn't have been playing with at our age. My mother restricted video games at home so at friend's homes we'd all go nuts 

None of us became psycho killers - one in fact is now a doctor. Kids do weird stuff in fictional settings. It's more often than not just morbid curiosity . The whole motivation in "Stand by Me" is a bunch of preteens wishing to see a dead body.

What worries me is how she treated your son. Her dad needs to discuss this with her asap. Acting like that towards a peer is already one thing but treating a one year old like that? That's insane. 

I also agree with left out- if you don't feel right about her actions do not leave your son alone with her. Above on video games is my opinion but your gut instinct is far more important.

I agree with what Lady T said about the video games.

What she she said to your son sounds like something she's probably hearing from someone somewhere.  No 10 year old I know talks like that, so I would assume she's been told that or heard it somewhere.  10 year old girls can be strange!