On 28 September 2020, Webbe was charged with harassment of a woman between 1 September 2018 and 26 April 2020. She was placed on unconditional bail to appear at Westminster Magistrates' Court. Webbe was suspended from the Labour whip pending the outcome of the case. On 11 November 2020, Webbe pleaded not guilty.

The harassment was directed at a woman who was having an affair with her partner, and allegedly included a threat to send 'naked' photographs of the victim to her children. The threats also allegedly included Webbe saying "You should be acid".

Webbe was found guilty on 13 October 2021. District Judge Paul Goldspring, the Chief Magistrate, said her evidence was "untruthful", and that her defence was "vague, incoherent and at times illogical". A further hearing took place on 4 November 2021, when she was sentenced to 10 weeks imprisonment, suspended for two years, and 200 hours of unpaid work. The Labour Party had called on her to resign from Parliament at the time of her conviction, and she was expelled from the party on the day she was sentenced.

Webbe appealed against the conviction and the appeal hearing commenced at Southwark Crown Court on 19 May 2022. Her appeal was dismissed on 26 May 2022, though her sentence was reduced to eighty hours of community service, and compensation to the victim reduced from £1,000 to £50. The judge found that Webbe had not "made a threat to throw acid over" Michelle Merritt. The judge stated Merritt was an "unsatisfactory witness" who had "told lies". As Webbe's reduced sentence was not custodial, it did not trigger a constituency recall petition under the Recall of MPs Act 2015.

In February 2021, Webbe apologised after an investigation by the Parliamentary Commissioner for Standards found that she had broken the Code of Conduct for MPs by her late registrations of remunerations received for her role as a councillor in Islington. The Commissioner also noted the late registration of a payment received from a business.

Also in 2021, Webbe stated on Twitter that "Earth is overpopulated; there are too many rich people. To solve the climate crisis; the rich must be abolished", a remark that drew criticism in view of her £81,000-per-year MP's salary.