Professor told me up front that she normally doesn't write letters for students who haven't done as much work with her I asked a professor for a letter of recommendation for graduate programs and she mentioned that she normally doesn't write letters for people who haven't done research with her. I took advanced classes of hers and did well though, and she agreed to write the letter, although hesitatingly. She mentioned that she normally only writes letters for people she's known for a while, so even though I did well in her coursework, am just now embarking on research with her, and have a history of tutoring for her class, it doesn't seem to be enough in her eyes. She also mentioned that she would have me write most of it and that she would basically just sign off on it.

Is this a warning sign? Should I turn to someone else to write the essay? A lot of the professors I've had left the university or were not full time professors, which is why I don't think they would be good people to ask for letters, so it's really hard for me to find recommenders right now that would be appropriate. Any advice would be appreciated.

Edit: Wanted to clarify that she seems like she had good intentions--she was willing to expand more on my teaching and ability to convey higher level concepts to new students, but that this type of letter is not the kind of letter she normally writes. Having seen the opinions of everyone, what is a good way to gauge whether or not she actually wants to write the letter?
Suggesting that you write the letter and she will just sign it could be the professor's way to drive home the message that she does not want to write this letter of recommendation. I feel she is really unwilling to write the letter and probably hesitatingly agreed either because you were insistent or because she felt an outright refusal might seem rude. It would be better not to push her to do something that she does not want to. In your place, I would definitely look for another professor.