Monique Kieuoanh Nguyen, 29, is accused of abusing a 17-year-old male student at a Sydney school between January and April 2024.
Arrested on May 22, 2024, she was originally charged with sexual intercourse with a young person under her care.
She has since been hit with nine further charges of intentionally sexually touching the boy and one charge of inciting him to touch her.
This alleged misconduct was uncovered by the teen's father who alerted police, Parramatta Local Court was told on Thursday.
"The father in that family, regularly - I think monthly - downloads the messages of each person in his family and reviews them," Nguyen's solicitor Mickaela Mate said.
Ms Mate argued her client should be repaid her "quite significant" legal costs.
Despite multiple adjournments and legal work done for the past six months, prosecutors still did not even know how many charges would be laid, she said.
"To put it in plain English, I just can't believe how it's taken them this long."
Nguyen's phone records of chats with the student would have been obtained by police in May 2024, she told the court.
Instead her client had to deal with allegations coming at her at a staggered pace without being told beforehand that the case had to be adjourned.
Nguyen was allowed to watch the proceedings by audiovisual link from what appeared to be a classroom containing a whiteboard.
Crown prosecutor Matthew Dickinson said the Director of Public Prosecutions had only been given the phone records of the alleged victim six months ago.
Technical difficulties prevented the DPP from opening a digital version and police had to provide 16,500 text messages in hard-copy, he said.
It had taken time to review all those messages, Mr Dickinson told the court.
Further charges could be laid, including in relation to alleged child abuse material after at least one reference to the boy's genitalia was found in the texts, the court heard.
Magistrate Peter Feather declined to award Nguyen's costs, noting the length of time required to read all the messages.
The matter will return to court on July 17.
1800 RESPECT (1800 737 732)
National Sexual Abuse and Redress Support Service 1800 211 028
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