The problem is the agent did not look out for your best interest. As a sellers agent she was good, as a buyers agent she failed. By all means you should have had a walkthrough and could have refused to sign until the house was cleaned. At very least the agent should have walked through the house knowing it was like this and warned you.
At this point it is an old wound, she didnt look out for you once i wouldnt give her a second chance. No matter what anyone says, an agent cant represent two people, they can however be fair and do what is right and what is ethical.
To find a new agent you should contatc other leading realtors in the area, look in your local paper, search Trulia or ask others if they have any referals. Before signing meet with them, ask them what they can offer, what their costs are and let them know what you expect out of tehm as your agent.