Final answer:
Hannah regretted not telling Rachel she would be her best friend because she felt there was nothing else for her to do. The consequences of her actions may have affected their friendship.
Step-by-step explanation:
Hannah regretted not telling Rachel she would be her best friend because she felt there was nothing else for her to do in that situation. Despite the regret, she would still act in the same way if given the chance to repeat it. The reason for her regret may be due to the consequences of her actions and the impact it had on their friendship.