It took me a long time and several sponsors to figure out that the best sponsor is one who sits down with us immediately when they agree to sponsor us and has us both talk about expectations in the relationship. Such as how often phone calls are to be made, who is to make those phone calls, when is it ok to call (hours of the day or night), what reasons should prompt us to make a call, the sponsors availability, what do we want or expect to learn while they are our sponsor (our goals), what are their goals for the sponsorship, religious beliefs and how that applies to their sponsorship (do they expect me to conform to their beliefs of a Higher Power?), etc...
It sounds like that was not the case with this sponsor. My personal opinion is that if she said she would call back she should have either said it would be later when she had more time or she should have called back promptly and that to leave you hanging was not acceptable behavior. No matter how much time we have in the program none of us are 100% well and we all have our faults just as any human does. What sitting down with a sponsor does is helps us figure out if we can accept and work with those behaviors.
A good book to read that will help you figure out sponsorship and how to pick a sponsor, be a sponsee, or how to be a sponsor is "Twelve Step Sponsorship, How it works" by Hamilton B. It can be picked up at most serenity shops or amazon.com. I would be considering talking with this sponsor and asking some of the above questions to figure out if she is going to be a good fit for you. If not then it is time to find someone who will be a good fit.