Thanks for writing in.
In my opinion, your niece has a lot of anxiety
which is leading to repeated vomiting
. She needs to take it easy and practice some meditation
. She also must eat a healthy and balanced diet and avoid excessive tea/coffee. Regular exercise will also help a lot. You must help her in this stressful period. The family should support her every step of the way and not put any pressure on her to do well.
Hope this helps