I am not a CA criminal lawyer, so I will defer on your question regarding criminal fraud. It's seems that you probably should pursue breach of contract, fraud, misrepresentation, and possibly other theories of liability available under CA law. These are civil liability theories in which your recovery is money damages. They do not involve arrest or criminal charges. There are many very capable CA litigators and contracts lawyers on AVVO who can provide more detailed analysis of your situation.
Assuming there is proof that she lied about her employment status, yes you could be arrested for some version of theft by deception. My experience with CA law enforcement is they really don't have any budget for small stuff and would tell you to go civil. Unless you can show some pretty big amounts you will find yourself in Small Claims court where attorneys are pretty much excluded. Find out if San Diego City Clerk can get you information on her business license. Cities LOVE to find out about people operating without a license. The County may also come in to get their business personal property taxes as well. All that feels good but does not get you reimbursed. Overall, your greatest problem is your lack of big dollar damages to attract a lawyer.
I agree with my out of state colleagues. While what was done may technically be a crime, it is highly unlikely you will get the police to arrest her or the DA to prosecute her. They both will tell you to use your civil remedies. Your civil remedies are you ability to sue her. You can also report her to LA Fitness, who will likely fire her immediately.
Good luck to you.
This answer should not be construed to create any attorney-client relationship. Such a relationship can be formed only through the mutual execution of an attorney-client agreement. The answer given is based on the extremely limited facts provided and the proper course of action might change significantly with the introduction of other facts. All who read this answer should not rely on the answer to govern their conduct. Please seek the advice of competent counsel after disclosing all facts to that attorney. This answer is intended for California residents only. The answering party is only licensed to practice in the State of California.
Assuming your alleged damages are less than $10,000, small claims court is your best bet at redress in this scenario. Good luck .
The information/answer is not, nor is it intended to be, legal advice. Consult an attorney regarding your individual situation. This attorney is only licensed to practice law in California. Your question and this answer do not create an attorney-client relationship. Do not send/post any confidential information.
Go ask LA Fitness for a refund since she was their employee; threatening to have people arrested though will likely not be a productive tactic.
This is not legal advice but a general comment on society. International Law 24/7 hotline +1-202-318-2406 - Dr. Jonathan Levy, PhD calls or emails usually returned within 24 hours.