The gofundme fundraiser has received more than 1,700 individual donations as of Thursday morning following the shocked reaction to the death of Belly Mujinga.
The 47-year-old was on the station concourse in March when a member of the public claiming to have Covid-19 spat at her and her colleague.
Within days of the assault, both women fell ill with the virus and Ms Mujinga, who has an 11-year-old daughter and underlying respiratory problems, died in hospital in Barnet 11 days after the attack on April 5.
British Transport Police has now launched an investigation while her union the Transport Salaried Staffs Association (TSSA) said many of its members were now fearful for their safety.
Officials contacted Ms Mujinga's employers, Govia Thameslink Railway, on Thursday, calling for greater protection for workers.
The union said staff should continue to work in ticket offices and not be made to work on concourses, and should be given proper protection.
Workers with underlying medical conditions should be stood down immediately, and any assault on staff should be investigated, the union added.
Ms Mujinga, who had an 11-year-old daughter, was approached by a man who identified himself as being infected with Covid-19 as she worked on the concourse at the London transport hub on March 21.
She subsequently fell ill and died in Barnet hospital on April 5.
Speaking during Prime Minister's Questions on Wednesday, Mr Johnson described the death of Belly Mujinga as "tragic".
He said: “The fact that she was abused for doing her job is utterly appalling."