That law isn't new. GA relaxed their business records laws about 4-5 years ago. Made it VERY easy for junk debt buyers to avail themselves of the court with an affidavit and photocopies.
It is all one company even if they have different names. Midland Funding and MCM are both owned by Encore Capital.
The argument should have been that she cannot attest to the records of Barclays but if the Magistrate was simply going to rubber stamp a verdict for the Plaintiff there is little you can do to fight it.
If you appeal in GA it is a trial de novo meaning it starts over as though Magistrate Court never happened. I would consider it but you only have 30 days to file the appeal.
GA relaxed their business records laws about 4-5 years ago after significant lobbying by creditors especially Freddie Hanna, Inside Arm and the give 5 junk debt buyers. Now all the Plaintiff has to do is send a letter stating the Defendant has the opportunity to come to their office and "review the documents intended for trial" and if the Defendant doesn't do this they lose the right to challenge them as hearsay at trial. Even affidavits.
Hall County where the OP is from is very small town good ole boy justice where you have little chance in Magistrate Court if you are not a "friend" of the court and most collections lawyers are their hunting and drinking buddies.
It is if the court agrees with your challenge. Magistrate Court is kind of a hit or miss proposition in GA. You cannot do discovery without special permission from the court and it is rarely granted. Waste of time to file a motion ahead of time as well as EVERYTHING is done on the day of trial. Once you are served and answer you will have a trial date that happens within 30 days and in smaller counties as fast as 2 weeks. Many Magistrates have no legal experience at all and are merely popular elected officials who enjoy wielding their power doing favors for their buddies. Welcome to the South.