According to police, Guastaferro -- who appeared on "Swap" back in '08 -- was in a car with a 54-year-old lawyer who was arrested for DWI near Buffalo, NY on August 27.
The lawyer was also busted for providing alcohol to a person under 21 (Alicia) and patronizing a prostitute (also Alicia).
The lawyer has since denied any wrongdoing.
According to reports, Alicia told police she's known the lawyer for 2 years ... and he usually pays her between $500 and $700 for sex.
FYI -- Guastaferro sued the people behind "Wife Swap" in 2010 ... claiming the show made her look like a "spoiled brat." The case is still ongoing.