A Victorian teacher who started a sexual relationship with her student while he was grieving the death of a friend will not spend any time behind bars.

The 31-year-old woman first sought out the boy a week after his friend died in a crash.

She gave him her Instagram handle and the pair began sending friendly messages which quickly escalated into texts about love.

They met in private a month later when the teacher told her student she knew it was wrong to see him.

He began sneaking out of his house at night and she would drive them to a nearby forest where they had sex in her car.

Later he started going to her house where the sex continued.

The offending came to light when their secondary school in Victoria's Gippsland region received two anonymous letters about the inappropriate relationship.

The woman this week pleaded guilty in the County Court to four counts of sex with a 16-year-old who was under her care or supervision.

She was to be sentenced on Friday but Judge John Smallwood said he was still grappling with the objective seriousness of her offending.

He noted the boy was aged 16 and had told police his teacher had treated him well and he regarded her as a friend.

Prosecutor Andrew Moore told the court while there was no direct evidence of harm, that did not reduce the seriousness of the offending.

"It is a notorious fact in these sorts of cases ... that harm doesn't surface until a little later and sometimes even decades later," Mr Moore said.

The boy was trying to forget the incident and focus on work instead of speaking to a counsellor, the prosecutor said.

Judge Smallwood accepted the case was serious but said he was still unsure of the sentence.

"The crime is the breach of trust, not the sexual act," Judge Smallwood said.

"That's what I'm struggling with."

The judge was also concerned about the lack of comparative cases, telling the woman he did not want to "make a guinea pig out of her" given the "sheer fragility" of her mental state.

The court was told the woman had post-traumatic stress disorder, borderline personality disorder and had recently been hospitalised because of suicide attempts and ideation.

Judge Smallwood told the woman she would not be jailed over the offending but he would need more time to decide on her exact sentence.

He adjourned the case to a date to be fixed, asking the prosecutor and woman's lawyer to search for information about similar cases.

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