Stress becomes more intense as Nina becomes jealous of other dancers. A ripped toenail while practicing her thirty-two fouettés occurs due to her stereo type of a 'strained dancer'.
She becomes desperate as her dancing becomes more extravagant and dangerous.
In Nina’s mind Lily is trying to steal her role and steal her glory but this is not true.
She has feelings of threat and vulnerability brought upon by other dancing causing stress, as Lazarus says.