Investigators on both sides of the border, however, doubt that version of events. Christos Salis and Eleftheria Dimopoulo, the Greek Roma couple who raised Maria from a few months old, are still in custody charged with kidnapping.
And on Friday afternoon, Bulgarian police said they had launched a criminal investigation on suspicion the Rusevs had sold Maria for illegal adoption.
Law enforcement sources in Greece say Bulgarian women have in the past been detected traveling heavily pregnant into Greece. They say once they give birth they pass their children off to childless Greek couples for an agreed payment.
Underscoring those assertions, Greek police said Friday they had arrested a non-Roma Greek couple in Athens on charges of trying to buy a Roma baby for 4,000 euros ($5,500).
Investigators have not given any hint how long it may take to prove or discount their allegations that Maria may have been the victim of an illegal adoption.
What is immediately clear, though, is that she, like many Roma children, is a victim of crushing poverty. The European Union says of the estimated 12 million Roma in the EU, 90% live below the poverty line.
In Nikolaevo, many inhabitants say they, like Maria's parents, regularly travel to Greece to harvest fruit and vegetables.
In Greece, impoverished Roma in the camp where Maria was found say they are now faced with competition for farm jobs from Bulgarian, Romanian and Albanian Roma who are even more desperate than them and ready to work for as little as 10 euros a day.
As I said goodbye to Katia, she asked if Maria would be allowed to come home to the family.
"My mother really wants her to come and live with them. She's been crying, and she's so worried," she said.
For now, there seems little immediate prospect of a family reunion.
Bulgaria's Child Protection Services went to Nikolaevo on Friday to carry out what they said was an assessment of Saska Ruseva's "suitability as a parent" and the family's living conditions.
By nightfall, the same state officials were back with police to take Angel and Minka into protective care.
A female relative had taken in the youngsters. She began to wail loudly at the prospect of the adolescents being taken away.
Just then, we saw another neighbor dodge past the police officers and help Angel and Minka slip away into the night.