Model's hand should look like she's holding a coffee plate. (check target look)
She can try to cross her legs the other way too, I'm not sure which pose would look better, we can choose later the best version.
The chair height is ~45cm, but if you don't have anything like that in the studio it's ok, I can adjust the dimension in 3D, but an armchair can't be very big (the sit level is actually a little lower than on a stool, that's why I had to make the stool smaller and now it looks funny).
You can place her on whatever object is closer to that height - a box, a speaker, it doesn't matter as long as it doesn't cover her body.