first of all you need to mention what birth control method you both are following, accordingly we can justify the possibility of pregnancy
All birth control measures are not hundred percent effective.
pregnancy can be ruled out by a simple urine pregnancy test.
the symptoms you are talking about is vomiting and diarrhea
which can very well be related to gastroenteritis
or food poisoning
so first , kindly give her some symptomatic treatment for vomiting and diarrhea followed by a pregnancy test.