Journey Guitarist Neal Schon -- Battle With Ex-Mother-In Law Rages On

Girl can't help it ... she has a right to speak her opinion ... so says the ex-mother-in-law of Journey guitarist Neal Schon, who's using the constitution to fire back at his defamation lawsuit.

Schon's been battling Judy Kozan in court since March -- claiming Judy's been trashing him online for years and falsely accused him of being a deadbeat dad. He sued for at least $75,000 is damages.

FYI -- Judy is the mother of Amber Schon, whom Neal divorced back in 2007.

In court docs filed earlier this month, Kozan claims anything she wrote online in her blog is protected under the First Amendment. Not only that, she claims she NEVER mentioned Schon by name, therefore she can't be held responsible for tarnishing his rep.

Judy is asking a judge to dismiss the suit ASAP.