As much information as you have.
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Provide a brief description of the crime. Practice writing it a few times, making it clearer and clearer each time. Do not "vomit" up a million facts that are irrelevant. It is disrespectful to put too many facts down, as if you are saying, "I don't know what is relevant, so here it all is - you figure it out." Do not do that. You will anger the reader.
Include a reference to your bank statements and highlight in yellow those transactions that your ex is responsible for. Be sure to emphasize that you did not consent or agree to her use of the funds and that you certainly want the money back. I trust you have contacted your bank to file a fraud report and if you have not, please do so. Good luck.