And she found the company had dismissed her unlawfully because she was pregnant, took annual and personal leave to which she was entitled, and was temporarily absent from work on account of illness.
Australian employment laws protect workers from being sacked on any of these grounds, leaving companies that do so open to being ordered to pay compensation.
Mahajan had told her boss she was pregnant at her three-month probation meeting, the court heard, advising of her intended dates to take maternity leave.
She took seven days of sick leave plus four days of annual leave due to morning sickness and medical appointments.
She told the court she had been "five to 10 minutes late" for work on a handful of days due to public transport delays, and would make up the time at the end of the day.
Her manager, the firm's principal, Tim Perrin, seized on this as a reason to sack her, the court heard, claiming that she had shown a "pattern of failures to attend work punctually" - but conceded under cross-examination that the company had not raised performance concerns with Mahajan at her three-month review and had indicated that he was "happy with how she was going".
COURT REJECT EMPLOYER'S ARGUMENT
"It beggars belief that Mr Perrin would have said that the applicant's employment had become unreliable on the basis that she was a little late for work on six or seven occasions in a three-month period, in combination with some formatting issues that he had not previously raised with her in a formal manner," the judge said in a written decision.
"It is also preposterous that the applicant could have been dismissed for sometimes not picking up discrepancies in valuation figures. The primary responsibility for that sort of error obviously lies with the valuer who prepared the report."
The company had told the court it had concerns about Mahajan's competency in formatting valuation reports and ensuring consistency in valuation figures.
Minutes tabled in court from an April 2016 directors' meeting detailed a discussion about other staff members with performance issues, along with a note about Mahajan which read: "6 months 6 June. Situation needs to be dealt with".
Riley rejected Perrin's claim that Mahajan's "lateness" was discussed at this meeting, as the minutes did not support this and she did not find Perrin and his fellow directors' evidence on the issue to be persuasive.
Perrin told news.com.au he was "disappointed" with the outcome of the case, and said he would decide whether to appeal once the court had assessed the amount of damages the firm would have to pay to Mahajan.
News.com.au has sought comment from Mahajan through her legal representatives.