5:26 PM PT -- A rep for Netflix tells TMZ ... "We intend to defend this matter vigorously and to stand by Richard Gadd's right to tell his story."

The woman believed to be the real-life inspiration behind the villain in "Baby Reindeer" is now taking Netflix to court -- claiming they defamed her ... and she's gunning for millions.

Fiona Harvey just filed a suit against the streaming giant -- and she's flat-out denying many of the actions Martha allegedly did in the limited series ... in which she's painted as an overly-obsessed stalker constantly hounding the main character, played by Richard Gadd.

In the docs, obtained by TMZ, Harvey alleges that Netflix created an easily accessible road map to allow viewers to track her down in real life and connect the dots to her identity.

She says Netflix included a lot of real phrases she'd said to Gadd -- many of which were documented on her social media pages -- and also used very similar descriptions of her job (a lawyer) in what she claims was minimal effort to mask her from the public.

As a result, Harvey claims she's been bombarded by people all over the world -- whom she claims are harassing her because of the show and how Netflix portrayed her on TV.

More importantly ... Harvey claims that Netflix completely ruined her rep with false and defamatory descriptions via their Martha character -- with FH flat-out saying in her docs that she NEVER stalked Gadd, never sexually assaulted him and is not a convicted stalker.

The show depicts the Martha character as doing and going through all these things -- and Fiona claims Netflix has led the public to believe this is all factual and about her ... which she says is BS.

Harvey says Netflix failed to do its due diligence in getting the true story -- and because of that ... she says they oughta be on the hook legally. She's suing for defamation, negligence, intentional infliction of emotional distress, violations of right of publicity and more.

She's seeking more than $50 million in damages.

We've reached out to Netflix ... so far, no word back yet.