Wiz Khalifa’s Mom Files $50,000 Defamation Suit Against Ex Daughter-In-Law, Amber Rose .

Wiz Khalifa’s mom, Katie Wimbush-Polk, has a problem with her son’s ex-wife, Amber Rose, and apparently it’s a lot more serious than a quick sit-down can fix.

Sources close to Amber tell TMZ … Amber’s furious that Katie Wimbush-Polk‘s hatred for her has spilled into the courtroom. Katie has sued Amber for defamation, claiming Amber’s allegation Katie’s an unfit grandmother is a big fat lie.

We’re told Amber believes it’s just a revenge lawsuit because Katie can’t let go of the fact Amber left her son 3 years ago, and Katie has tried to make Amber’s life a living hell ever since the split.

Katie’s also taken shots at Amber on social media, ripping her to shreds every chance she gets … like in 2015 when Katie jumped into the KardashianAmber beef and defended the Klan.