The Buddha was a bodhisatta in his many previous lives before His last life as prince Siddhattha. The future Buddha Metteyya also has to fulfill His bodhisatta function before becoming the future Buddha. While Kuan Yin wasn't specifically mentioned in the Nikayas, someone somewhere is following the bodhisatta path to carry on the great Buddhas lineage. Anyway, if someone prayed to Kuan Yin everyday but s/he never abstain from killing, stealing, sexual misconduct, lying, and taking intoxicants then it'd be difficult to see how the bodhisattvas and other deities would be able to help that individual when his/her unwholesome kamma bears fruit. So it all has to start with the individual's efforts like observing the five precepts, the eightfold noble path, the brahmaviharas, etc.. These are the foundation that all Buddhist schools share in common. So next time if one prays to Kuan Yin wholeheartedly and have yet to see any result, s/he should start with the foundation mentioned above first..