From your query it is not very clear whether your daughter just skips some meals or is in the habit of secretly eating food and then vomiting it out. If the latter is the case, then she needs to be immediately examined for an eating disorder by a nutrition expert or a doctor. Eating disorders are common during adolescence but should be taken seriously and professionally treated. However, you have mentioned that she likes to eat junk food, which is a fad among adolescents and nothing to be unduly worried about. She will gradually get over this phase of defiance and irritability. You can help her best by not being too disapproving of her behaviour and eating habits. Do not be too demanding of her at this time and give her time. Having said that, set reasonable limits for her too. Make sure that she eats at least one meal at home and preferably the whole family should eat together. Having company at the dining table usually makes children eat better. Monitor her eating habits closely without being too intrusive and if she is not purging out her food then things should be fine. Do not worry about it too much.