Circuit Judge Robert Dugan rejected arguments Wednesday by a lawyer for Stephanie Mikles, 46, that the law banning "unnatural or perverted practice" is so vague as to be unconstitutional, The Baltimore Sun reported.
The judge called the law "poorly drafted" but said his job is not to grade the state legislature's work.
Mikles, a Jarrettsville resident, is a former behavioral specialist with the Harford County Public Schools in the Baltimore suburbs.
Her legal problems began in 2008 when a boy accused her of sexually molesting him. While she was not charged in that case, investigators searching her home found a video showing her having sex with the dog.
During a lengthy hearing, defense lawyer Leslie Gladstone argued Mikles should be charged at most with animal cruelty, instead of a crime that carries a penalty of as much as 10 years in prison.
"If someone chooses to have, as the state alleges, sex with an animal, is that something the state has the right to criminalize because they believe it is immoral? I believe the answer is no," Gladstone said. "The state should not attempt to define the meaning of a relationship or to set its boundaries, barring injury to a person, and there is no allegation of injury."