Lee Furlong, 23, was arrested alongside Canadian Brittney Schneider, at a guest house in Chiang Mai in Northern Thailand. "This is out of character for her".
Brittney and her friend Furlong Lee have admitted to defacing the ancient wall.
Tha Pae Gate, which dates back to the 13th century, is part of an historic wall that forms a square around Chiang Mai's inner city.
"They admitted to the crime", according to police Major Anon Cherdchutrakulthong.
Tara said her daughter "made a mistake".
Migrant Caravan Masses Near Mexican Border
The much talked about caravan of Central American migrants has been forced to turn around at the Mexico-Guatemala border. The group chanted: 'We are not smugglers, we are migrants, ' as they reorganized themselves on Friday afternoon.
Schneider said her daughter won't be able to leave the country until the trial so she will fly to Thailand as soon as possible to be with her.
She said she is overwhelmed by the charges against her daughter. She's sorry for what she done. She said that the "routine" action, which looks like a march of shame, would have been the case if it was domestic or foreign-born suspects.
"You would have to know Britteny to know this is not her", said Schneider. "But I said stay strong and breathe and go through it". "It was an act of being intoxicated".
Video obtained by Reuters showed the words "Scouser Lee B" painted on the wall in an apparent reference to the English city of Liverpool.
The pair face up to 10 years in jail, a fine of up to one million baht ($30,656) or both, if found guilty, police said. Police did not confirm Mr Lee's hometown.