You liked the agent, you listed the house and then you never saw her again.
If she hasn't broken the terms of your contract, you're stuck with her until that three- or six-month contract ends.
The key here is that if you don't want to end up stuck with an agent who doesn't have the skills to sell your house, you can ask a fair number of questions up front. You can -- and should -- write your expectations into the contract. And if you find an agent who's unwilling to alter that preprinted form for you to sign, then find someone who will.
It's hard to sell a house right now. Credit is tight, prices are falling and sellers have had to bring down their expectations rapidly in the last few years. Further, if you're trying to do a short sale, you need someone who has the experience to negotiate price with several parties who may be holding different parts of the loan that's in trouble.
Asking questions like these can help: Can I have some references? Have you ever negotiated a short sale? When was the last time you sold a house?
For more specific methods of evaluating an agent, read on.