"However there's a code of conduct which she has been made aware of and should she infringe that she is risking her job and the right to return to school."
The 33-year-old English teacher bared her body to the cameras when her towel fell as she stepped out of the shower - and she has also been seen kissing fellow housemate Paul, 25, in the garden.
Ms Tooley said: "I haven't seen this display of nudity myself, I've only heard about it - I understand that it was an accident and the towel slipped.
"However there's a code of conduct which she has been made aware of and should she infringe that she is risking her job and the right to return to school."
Ms Tooley said that when the Big Brother series was over, Ms Ellis would have to report to her.
'Role models'
"At that stage I will have made a decision in consultation with the school governors and the local education authority legal team about how her behaviour has infringed our code of conduct and what the resulting position will be.
"I have to make sure that the profile of the school and its ability to provide positive role models for my girls is maintained."
But Ms Tooley went onto praise the contestant's work as a teacher.
"She is a very hard working person who organises a lot of extra-curricular activities.
"She spends weekends and after school hours doing this and spends a lot of her lunchtimes providing extra-curricular help for students.
"I would be very sorry to lose her and hope that she does come back - but I will respect her decision to move on and do different things," said the headmistress.
Nigel de Gruchy, general secretary of the National Association of Schoolmasters Union of Women Teachers (NASUWT), advised any member of his organisation against appearing nude on television.
"I don't know if this woman is one of our members, but if she is I would say it was inadvisable for her to do something like that if she is interested in keeping her job," he said.
Channel 4's Big Brother 2 looks on course to repeat last year's ratings success, drawing more than four million viewers on Monday night - just three days into the series - equal to the first series at about the same stage.