Left A Negative Review After Paying For A Service That Didn't Work As Advertised; Now Being Sued For Extortion And Defamation

My mom is in her 70s and she lives in Florida. She saw an ad in the local paper that promised non surgical body slimming with immediate and permanent results in one visit; the owner claims to have patented and developed the procedure herself. The ad further stated if there aren't any visible or measurable results you don't pay. She called the business and the owner quoted a price of $1500. My mom went and had this procedure done and needless to say, it didn't work. She told the lady it didn't work but the lady insisted she had to give it time to drain. She said she was in a rush and needed my mom to sign a bunch of paperwork. When my mom started to read it, the lady stopped her, and insisted she just sign the forms. For whatever reason, my mom did. The owner charged my mom's credit card and provided no receipt, no copies of any signed documents, and no aftercare instructions.

A few days later my mom realized she was charged $2500 instead. She asked for a partial refund of $1000. The lady did not respond. A few days later she told the lady she disputed the charge, said she had waited for it to drain and still didn't see results, and again asked the lady to work with her. She invoked the business' refund policy and said if she didn't get a refund per the policy since she didn't have results, she would write "her own reviews online." The lady responded and threatened legal action. TL;DR - my mom posted reviews online and the lady sent her threatening texts demanding she take them down. The lady also told my mom she has sued everyone who has left reviews and "lied just to get the money back." The lady also began accusing my mom of posting reviews under aliases, which isn't true. My mom doubled down and updated the reviews to include her opinions that this lady is a liar (lady was publicly saying my mom lost 4.5 inches in this 1 hour treatment), a thief (other reviews claimed this lady also took money from them and refused to refund them), and is crazy. (I told her she should not have done that).

This lady just sued her for defamation and extortion and is seeking damages "in excess of $50,000." No evidence, statements, or exhibits are attached to the lawsuit. We also have reason to believe this lady is not licensed to perform these medical procedures in the state of Florida, but I'm not sure if that's relevant.

I have called a few attorneys and the advice has been discouraging; some say this will be very expensive and that my mom shouldn't have written what she did. My mom is on a fixed income and really can't afford to have a long drawn out legal battle. What should she do to have this case dropped?