The pair went to see a movie together on the day in question.
"There's nothing unusual or inappropriate about this," Mr McCaughan said. "Social workers were encouraged to spend time with the teenagers. What you might think was unusual was what took place next."
He told the jury Joseph put her head on the teen's arm and rubbed his stomach and chest under his T-shirt despite his protestations.
Afterwards, the pair met the complainant's mother at a restaurant in Mangere.
The Crown said between lunchtime and 10pm the two women consumed a large amount of alcohol.
Joseph eventually dropped the boy's mother at her house and drove to Oakwood Manor motor lodge with the complainant where she booked a large studio room.
Mr McCaughan said the teenager would give telling evidence of what happened in that room.
Initially he was watching television but Joseph allegedly asked him to come to bed.
"Once on the bed they started kissing and one thing led to another and they ended up having consensual sex together," the prosecutor said.
Days later, the complainant told another mentor what allegedly happened and the Waipareira Trust began an investigation.
Joseph admitted the pair had spent the night together but denied any sexual contact took place.
Mr McCaughan told the jury they would also hear extensive evidence of text messages between the pair that "really do illustrate the true nature of the relationship".
It is alleged the defendant called the boy "babes" during their communications and he would refer to her as "darling" or "my girl".
"If I told you exactly how I felt, I'd probably get sacked," Joseph allegedly texted.
Defence lawyer Paul Pati said their case was simple: "No sex or sexual contact occurred."
The trial before Judge Gerard Winter is set to finish next week.
