The woman was standing next to a fire in a drum on Sunday morning at the rally on farm land near Oturehua.
An unknown person threw accelerant on to the flames and she was caught in the flash.
She was later transferred to Dunedin Hospital by the Otago Regional Rescue Helicopter.
Brass Monkey Rally organising committee chairman Stan Hansen, of Dunedin, said he was disappointed no-one had notified him, or other committee members, about the incident.
He was also disappointed no-one had come forward with information about who had thrown the accelerant on the fire.
"I find it difficult to see how someone could throw accelerant on a fire like that without being known to the people standing around it."
Mr Hansen said the incident would be one of several discussed at the debriefing.
"We've got to look at the safety aspects of the rally but they've got to be practical. If we said `no, there's not going to be drum fires now', people at the rally will just light their own little camp fires which would be dangerous near tents."
The woman is in a stable condition in Dunedin Hospital.
