Maybe the peeing accident un-nerved her... and she felt embarrassed.
How did the Teachers handle it?
At most preschools, it is asked that parents ALWAYS bring for their child's cubby, an extra pair of clothing. Tops/bottoms/underwear. Because at this age, it happens and is completely NORMAL.
At least at my Daughter's preschool, that is how it was.
The Teacher, when a pee accident occurred, just acted like nothing, not bringing attention to the child, would help clean off the child and change into clean clothing, and then back to class. The teacher would then put the soiled clothing in a plastic bag. The Teacher then would tell the Parents upon pick up, or call them personally. But not to demean the child, but just as an FYI.
My girl, at that age in preschool, had pee accidents too. Normal.
But in school, she had extra clothing already, which I brought to school for her. And which ALL the children had, in their cubbies, labeled with their name.
I would be interested to know, HOW the Teacher handled it... and did she then put your child aside... like a sore thumb, or just acted like nothing happened so as to bring no attention to the child nor embarrassment???
Because that, would affect the child.
My daughter, when she had pee accidents, was not an occasion where she had to apologize... nor to feel ashamed. I told her its no biggie and she is normal.. and all kids do that, still. She is not the only one.
Even in Kindergarten, kids can still have pee accidents.
Maybe, she is just feeling ashamed... and throwing-up is a sign of anxiety or stress, in a child or adult.
try talking with her, ask her how she honestly feels, not just saying something to please others or to feel ashamed. If it is still bothering her, then that's okay. Ask the Teacher about it... tell the Teacher it caused her anxiety/stress. Ask the Teacher how she handles "accidents" in class with the kids.
Often, talking about it with the Teacher WITH your child as a PART of the conversation...can help ally the stress/anxiety/fears in your child, regarding peeing accidents. That is what my daughter's Teacher did and I.... we talked about it TOGETHER, comforting her, and with "love" so that she did not feel ashamed...
All the best,
Susan