It seems you can work with whoever you please at this point.
The first part of your question is a bit confusing. "Agency Disclosure" and "Fee" are two different things. Although I am not a rental agent in Manhattan, what I understand is that typically the tenant pays a fee equal to a percentage of the annual rent. That requires a contract between you and your agent. It is implied that as you have a contract with an agent, they have a fiduciary responsibility to you and are acting on your behalf. Depending on how the contract is written, some agents will consider this also their agency disclosure. Some agents to be on the safe side will also have you sign an agency disclosure.
My questions would be, did the first agent discuss agency disclosure so you understood it and did she also discuss her fee? Just because she didn't actually have you sign something does not necessarily mean she was unprofessional. The big question becomes, would you have found this apartment without her? You might legally be able to use another agent, but is it the right thing to do?
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