Has she eaten anything prior to an episode of vomiting, has she had any milk for instance ,it could be something she cannot tolerate or is allergic to .When you say time time do you mean in the middle of the night or before bed ?
my 3.5 year old daughter does that to she will wake up and throw up some times in my car watching TV just random no fever nothing! i talked to my daughters Dr she said it can be a certain food she eats..from a bad dream..or even stress at home can cause it. she said to document it every time she does it document what she ate before if she was sleeping or what she was doing and to do that for about 3 weeks then go in..unless she is losing weight