Horner denies all allegations against him and was cleared of any wrongdoing by Red Bull following an internal investigation.
However, the matter has continued to hang over the team after documents containing messages supposedly sent by Horner were leaked in Bahrain and has since resulted in several key personnel being linked with moves away from the team, including Helmut Marko, Adrian Newey and Max Verstappen.
Horner’s accuser has been suspended by Red Bull on full pay and has filed a compliant to Red Bull over the decision, as well as the sport’s governing body, the FIA.
Now, according to a report by The Sun, a new barrister has been appointed for the appeal and is due to speak with the employee within the next few days.
The Sun also report that the evidence that she brings could also see Horner summoned for questioning again.
A source from The Sun claimed: “No one wants this to drag on any longer than it needs to.
"Red Bull has made it clear that once the appeal is over, they are willing to be fully transparent.
“They don’t want to do anything that compromises the process but when it’s done, the gloves are off.”
The Sun also state that the respective parties are unlikely to publish the full report or comment on the matter, having both sign confidentially agreements.