Where do I go in Pompano Beach, FL to find out if guardianship has been done legally & money is being monitored? I believe fraud is involved

As a guardian you report to the State annually. You must prove that money is only going towards care of the person you are guardian for. You must also show that they are being cared for. Dr visits etc. I agree you may need a lawyer. You could go to the County seat where the person lives and see if guardianship was granted.

You need the help of a lawyer to guide you now. Take the documentation you have. You can also call your local APS to see if they will open a case. You say the initial fraud was done "years ago". It may be late now to make these claims on something done years ago. Other than the police, Adult Protective Services, or an Elder Law Attorney to check on guardianship filings, there really is no help. If your brother is her POA and Guardian then of course he will be on all of her accounts and have the ability to invest in her interest. Does your Mother live with your brother and are he and his girlfriend and her son caring for mother in their own home? If so they well may have a care contract regarding payment to them.
Good luck. Hope you update us.

I'm not familiar with the court system in that area, but that's where you would start.    As an example, Michigan has District Courts, above that are the Circuit Courts, then the higher level courts.   Most likely guardianships would be handled at a circuit court level, the kind of court at which lawsuits above a certain monetary level are filed.   

You need to find the court that serves the area in which your mother lived, and where residence was established, at the time the alleged guardianship took place.   It might have been through a Circuit Court, or a Probate Court, which handles estate matters.   

Best source might be to locate the Florida State Bar, familiarize yourself with the levels of court, then do some research to find out which level would handle guardianship.

Some courts have online listings of civil matters, so you could then search by your mother's name to try to locate a guardianship file.    If Florida courts are open and staffed, a staffer could help you.

You can also search for Florida statutes on guardianship, and although statutes aren't easy to read, you hopefully could find something addressing the necessary steps to get guardianship, as well as the level of courts in which guardianships are handled.   

To prove the elderly financial abuse, you will need documentation, and the assistance of an attorney.     That's another avenue, depending on your own financial situation:   hire an elder law or estate planning attorney, either of which should have litigation experience.