Andreea Cristea, 31, was knocked from Westminster Bridge into the River Thames during Muslim convert Khalid Masood's murderous rampage on March 22.
She had been visiting London with her boyfriend, Andrei Burnaz, who suffered a broken foot in the attack.
Scotland Yard said Ms Cristea was receiving treatment in hospital but life support was withdrawn on Thursday afternoon.
Her death brings the number of innocent victims of the attack to five.
In a statement, Mr Burnaz and Ms Cristea's family said she would "always be remembered as our shining ray of light that will forever keep on shining in our heart".
"After fighting for her life for over two weeks, our beloved and irreplaceable Andreea - wonderful daughter, sister, partner, dedicated friend and the most unique and life-loving person you can imagine - was cruelly and brutally ripped away from our lives in the most heartless and spiritless way."
They said the money raised for her recovery would now be donated to charity, adding: "She would not have it any other way."
"There are no words to even begin to describe the crushing pain and emptiness that is left in our hearts.
"Our family, together with Andrei, are deeply touched and eternally grateful for the unimaginable efforts and never-ending dedication provided to her and us by the entire medical personnel of each and every hospital involved. Their kindness and empathy are beyond compare."
They added: "We would not have been able to live through these trying and tragically hurtful weeks without the support of the Metropolitan Police, the UK Government and every department involved.
"Our hearts and love go out to our two family liaison officers, Detective Sergeants Tony De-Wilde and Geraint Jones, who stood beside us every single step of the way. You were our lifeline and we will never be able to thank you enough."