How about saying, "I'd like to go over your phone policy again. When we spoke before you said you could return my call if I left you a message, but I did leave a message earlier this week and never heard back. I want to make sure I understood your policy. Should I not count on a call back from you? I would really like to know, because if it is not your policy to return calls, then I won't leave a message."

How does that sound? You just want to get her policy straight so you do not set yourself up for rejection by calling and not getting a response. I think it's very reasonable!