The following sites, books, and articles will help you explore relevant questions and to prepare if you are seriously considering becoming a Buddhist nun.
International Mahayana Institute
On the International Mahayana Institute website, you will find more information on how to prepare for ordination.
Sravasti Abbey
On the Sravasti Abbey website, you will also find information on how to prepare for ordination.
Preparing for ordination
Reflections for Westerners Considering Monastic Ordination in the Tibetan Buddhist Tradition by Thubten Chodron, Sravasti Abbey. Foreword by His Holiness the Dalai Lama.