The Met said it was “inappropriate” to comment on the discrimination claim.
The first hearing in her case is due to take place at an employment tribunal next week.
Ms Sandhu, who is of Indian heritage, is one of a very small number of female Asian police officers at senior levels across England and Wales.
Last year, there were six Asian chief superintendents and three officers at a higher rank; most of them were male.
The 54-year-old, who joined the Met in 1989, claims she would have progressed faster and further had she not been discriminated against over many years.
Ms Sandhu is being backed by the Metropolitan Black Police Association, which says it is concerned about the lack of senior female ethnic minority officers.
Mick Creedon, the former chief constable of Derbyshire Police, who acted as her mentor and submitted a statement to the misconduct inquiry, has also offered support.
Scotland Yard confirmed an employment tribunal case had been brought by a senior officer and involved allegations of “racial and gender discrimination”.
The force said: “At this early stage, we are unable to comment further around defending the claim.”
Friends of Ms Sandhu said she began the legal action “reluctantly” after the force started an investigation into allegations she had encouraged colleagues to support her nomination for a Queen’s Police Medal (QPM).
The QPM, which was introduced in 1954, is awarded twice a year in the Queen’s Birthday and New Year Lists and is given to serving police officers in the UK in recognition of distinguished service or outstanding courage in the line of duty.
Officers are not expected to nominate themselves and are not meant to contribute to or know about the process.
In June 2018, Ms Sandhu was officially informed that she was under investigation for alleged “gross misconduct” which, if proven, could have led to her dismissal. She was placed on restrictive duties.
But last month the inquiry concluded she had “no case to answer” and would face no further action.
Restrictions on her duties at work have been lifted.
The Police Superintendents Association, which supported Ms Sandhu during the investigation, said it was “deeply disappointed” it had gone on for 12 months.
Two other officers – a detective superintendent and an inspector – who were investigated for misconduct were also cleared.
Scotland Yard said: “The Met’s Directorate of Professional Standards (DPS) began an investigation into the conduct of three officers following an allegation they breached guidelines relating to the UK honours nomination process.
“The investigation concluded in June 2019 and found there was no case to answer for gross misconduct or misconduct in relation to any of the officers.”