Diaz received a 10-year prison sentence for 14 counts of aggravated sexual assault, one count of rape and one count of bodily harm while making child pornography.
The court heard they sold the boy - who is now 10-years-old - on the darknet, a part of the internet that can only be accessed using special software.
News agency DPA reported that the Freiburg state court sentenced the woman on Tuesday to 12 and a half years in prison and her partner to 12 years. The court ruled that the man, who had a previous conviction for child sex offenses, must remain in preventive custody after serving his sentence.
On Tuesday, the Freidburg court convicted the couple for forced prostitution, rape, sexual and physical abuse, humiliation and bondage in nearly 60 separate identified acts.
On Monday, the court jailed a Spanish man for 10 years for sexually abusing the boy repeatedly. Christian L. was sentenced to 12 years with preventative detention. Some of the abuse was filmed.
Berrin T, 48, the boy's mother and his stepfather, Christian L, 39, were sentenced after appearing as witnesses for the prosecution against eight men who raped the boy in separate trials earlier this year.
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The odd behavior led officials to believe the man was under the influence of alcohol or drugs, Oroville Lt. He was reportedly walking around shining a flashlight into his own face.
According to case psychiatrist Hartmut Pleines, quoted by Spiegel, the mother's claim that she was in thrall to her partner when she committed the abuse was false. In May 2015, the couple started abusing the woman's son, with the man at first offering the child cash.
The pair and six others were arrested last September.
The Freiburg court also ordered the two abusers to pay 42 500 euros (49 200 dollars) in damages to the boy and a young girl, another victim in the case.
The trial has also raised concerns that officials might sometimes wrongly presume that a woman is incapable of abusing her own child.
Local authorities have been accused of failing to protect the boy, who now lives with a foster family, as the mother's partner was supposed to be banned from having contact with children.