Relatives of a woman who hid her baby in the maggot-invested trunk of a car insisted on Wednesday that they had no idea of her secret, at a trial that has drawn horror in France.Rosa Maria da Cruz, 50, faces up to 20 years in prison for keeping her daughter hidden away until she was nearly two, leaving her with serious mental disabilities.Discovered in 2013 in the filthy trunk of a Peugeot 307, the baby Serena had also been kept in an unused room at the family home in the Correze region of central France.It was a mechanic who found the baby in the trunk after da Cruz, who is originally from Portugal, took the car to be repaired. Hearing a noise, he opened the trunk to discover the baby in a car seat, naked, filthy and dehydrated. She was surrounded by maggots and excrement.The trial, which opened on Monday, has heard remarkable testimony from relatives of how da Cruz was to all appearances a model mother to her three other children.Her partner Domingos Sampaio Alves insists he had no idea she had given birth to another child and kept it a secret.By way of explanation, he said he went only once a month on average to the small ground-floor room, under renovation, where da Cruz kept the baby much of the time.He also did not visit the car often, as he does not have a driving licence."I don't know why she did this," he told the court in Portuguese through a translator.The unemployed bricklayer was originally charged, but investigators concluded there was no reason to doubt his account.Other children 'perfectly raised'Da Cruz was released pending trial, and the couple have stayed together."I continue to live with her because she is a good mother to the children," Alves told the court. They have kept their three older children - aged nine, 14 and 15 - but authorities have refused to let them have contact with Serena, who is now aged seven and living with foster parents.In her opening testimony on Monday, da Cruz fought back tears and told the court: "It's very hard to be confronted with reality, with the damage I have done."Serena now suffers from severe mental impairments including irreversible autism which medical experts have linked to sensory deprivation during her early months. A paediatrician who examined Serena and her siblings after the discovery said her team had been "stupefied" by "the gulf between Serena's situation and those of her brothers and sisters", who appeared to have been "perfectly raised"."You could see she had been a good mother, and we could not understand why Serena had not received the same quality of care at home," the doctor said.Judge Gilles Fonrouge said that while the child was now in good physical health, she was "closed off to interactions around her".Marie-Pierre Peis-Hitier, a lawyer for social services, said the child could only say a handful of words, adding that it had taken a full afternoon to win the child's trust.In emotional testimony, da Cruz's sister and nieces also said they had no idea of Serena's existence, adding that she was a "loving" mother to the other children."Inside I think she is suffering. She knows what she has done," her niece Elodie told the court.The trial heard that da Cruz had initially hidden the pregnancies of two of her other children from her partner, not wanting to face reality.