What Causes Vomiting With Nausea?

my girlfriend woke up at 4AM saturday morning with vomiting and nausea. but has not had a fever at all. the last she vomited was around 12 saturday afternoon. what could this be from? i know that's it's common to have a fever but that's not the case here. she doesn't have any body aches or anything like that wrong with her. now, she ate mcdonalds chicken nuggets friday night before she fell asleep. could that be the cause?? that's the only thing that came to my mind, other than being outside a few minutes without a coat. and could this be contagious? i'm not sure if i should be around her or if i'm at risk to getting sick or not. she woke up this morning feeling fine and ate a full breakfast with no side affects. any advice please? thank you!