Thank you for your query at DoctorSpring.com
I understand your concern.
Before attributing it to PMS i need to know about her dates-
1) When was her LMP?
2) Does she always strong symptoms before getting her period?
3) How many days does she have bleeding in her regular cycles?
Vomiting, headache and nausea are more towards pregnancy than PMS, and it has already been ruled out. So it can also be due to stress. However based on your additional history, i can guide you further.