The unnamed woman, who accused the Red Bull Racing chief of abusive behaviour and sexual harassment, is said to be “determined for the truth to come out”.
Horner, 50, was cleared of misconduct by a Red Bull investigation back in February.
But the scandal was taken to a new level when sexually suggestive texts appearing to be sent by the F1 boss were leaked.
Horner’s accuser – a female colleague – has since been suspended by Red Bull and has appealed the decision.
She has been left feeling “very upset, angry, scared, intimidated and lonely” following the saga, a family friend told BBC Sport.
The insider added: “Every time I have asked her something, she breaks down in tears and says she’s got no-one to talk to because she’s not allowed to talk.”
The woman lodged a complaint with Red Bull in December and now “struggles to understand” how it was dismissed following an investigation, the pal said.
She plans to take her case to an employment tribunal as she wants to return to work for the championship-winning team, it is understood.
The friend added: “She is determined for the truth to come out.
“She just wants to work in the sport and is very concerned about her reputation and ability to get hired by anyone.”
Horner has always denied any wrongdoing over the allegations and blasted the infamous text leak as “anonymous speculation”.
He has demanded an end to the drama which he described as a “very trying period” for his family.
His wife Geri has stood by him – appearing at his side at the races in Saudi Arabia and Bahrain, both won by Red Bull.
At the weekend, the pair – who wed in 2015 – put on a united front at a Point to Point in Buckinghamshire.
But there is set to be more heartache for the Ginger Spice star as Horner’s sexting scandal is set to be covered in the next season of the hit Netflix show Drive to Survive.
Show chief James Gay-Rees has revealed his team plans to include the saga that rocked F1 in the documentary’s seventh season.
It will potentially reopen wounds for Horner and his wife as they attempt to move on from the drama.
Horner has previously raged against the scrutiny over the scandal – but now it will be the focus of the Netflix show watched by millions.
Brit filmmaker Gay-Rees revealed he has spoken to the Red Bull chief since the scandal broke before the start of the F1 season.
He claims the ex-racing driver told him: “This is all your fault.”
Horner appears to have been referencing the new focus Drive to Survive has put on F1 – especially drama and scandal behind the scenes of the Grand Prix circus.
SCANDAL… LAP BY LAP
FEBRUARY 5: A Dutch newspaper reports a female Red Bull employee has made serious allegations of “inappropriate, controlling behaviour” about Horner to parent company Red Bull GmbH.
FEB 9: Horner is quizzed for nine hours by the lawyer hired by Red Bull to investigate.
FEB 15: He denies the allegations and says they are a distraction for the team.
FEB 15: F1 says it hopes the matter will be clarified at the earliest opportunity after a fair and thorough process.
FEB 26: Red Bull’s engine partner Ford says it is increasingly frustrated by the team’s handling of the complaint.
FEB 28: Horner is cleared of all wrongdoing. The employee is said to have the right of appeal.
FEB 29: Horner says he is pleased the investigation is over.
FEB 29: WhatsApp texts and pictures claimed to be between Horner and the employee are sent to journalists and F1.
MARCH 1: Horner refuses to comment on what he calls “anonymous speculation from unknown sources”.
MAR 2: Horner and wife Geri are pictured hand-in-hand, as Red Bull’s Max Verstappen wins the Bahrain Grand Prix. Horner says before the race: “It’s been very testing for my family but we are very strong and our focus is on this race.”
MAR 3: Verstappen’s dad Jos, claims Red Bull is in “danger of being torn apart” if Horner stays in the job. He denies being the source of the WhatsApp leak, saying: “It can’t go on the way it is. It will explode. He is playing the victim, when he is the one causing the problems.”
MAR 6: Max Verstappen sides with his dad in the row.
MAR 7: Horner says he wants to draw a line under the scandal and hails Geri’s support — as Red Bull suspends the employee.
MAR 15: Horner’s accuser allegedly launches an appeal against the investigation that saw the Red Bull chief cleared.
MAR 16: The female employee lodges a complaint against Horner with the FIA.
MAR 17: Horner reportedly agrees to ‘public ceasefire’ with senior Red Bull Racing management to quell the drama