She also has more than one reason to be having irregular periods at this stage in her life. First, it is common for girls to have varied periods for up to two years after they have their first period, with more than half of their cycles not releasing an egg (being anovulatory). These different bleeding patterns may include several months in a row without any period, especially during the first year after menarche.
Secondly, athletes often have varied menstrual cycles due to substances in the brain that suppress a gland in the body that produces hormones (the hypothalamus) which causes no periods (amenorrhea). I do not know how athletic she is or how intense her participation is in sports. However, the lack of periods in your daughter, like other athletes, is felt to be associated with the intensity of her exercise, her body weight, and how much body fat she has. A body fat percentage of 22% is considered necessary to maintain regular periods.
In sum, your daughter seems to be having normal pubertal development. Having no periods (amenorrhea) for the last few months may also be normal. If your worries continue, discuss it further with her pediatrician who can complete a history, do an examination, and consider checking for other less likely explanations.