Spanish authorities have released few details about the case to protect the girl's privacy.
But in comments published Wednesday, her mother told reporters the baby's father is a 13-year-old boy who is still in Romania and is no longer going out with her daughter.
The 10-year-old girl and her baby daughter plan to stay in Spain because the young couple separated, said the girl's mother. She identified herself only as Olimpia and appeared to be in her 30s but did not give her age.
She also said she didn't understand the attention the case was generating because she and her daughter are Romanian Gypsies, or Roma, and their custom is to allow girls to marry young even though that's against the law in Romania.
"That's the way we get married," the girl's mother told reporters Tuesday outside the modest apartment building in the southern town of Lebrija where the family lives.
Meanwhile, the story was going viral on the Internet and causing an uproar in Spain.
"Mother at 10 years old" blared a headline in Barcelona's La Vanguardia newspaper, which dedicated two pages to the story.
In contrast, news about the 10-year-old mother barely registered in Romania, with stories buried inside newspapers focusing on the controversy the birth had caused among Spaniards.
The girl moved to Spain about three weeks ago, her mother said, and her baby was born in a public hospital last week in the nearby city of Jerez de la Frontera. There were no complications during the birth, and the 10-year-old and her baby are doing fine, her mother said.
"She's doing well and is very happy with her daughter," the woman said.
The 10-year-old and her baby are living with the new grandmother while Spanish social welfare authorities determine whether the family will be able to provide for the baby.
Under Spanish law, having consensual sex with someone under age 13 is classified as child abuse. But a Justice Ministry official said this particular case is complicated, because the alleged father is not in Spain and is also a minor. It is not clear whether he could be charged, said the official, who spoke on condition of anonymity because of ministry policy.
Romanian law allows girls to get married at age 16 with parental consent, or at 18 without it.
But arranged "marriages" between teenagers are relatively common among Roma, who make up about 1.5 million of Romania's 22 million people. Families "marry off" daughters when they reach puberty, with the "husband" usually being a couple of years older. The marriages are not recognized by the state.
Roma girls are often not encouraged to pursue a full education, and Romanian authorities do not widely enforce education laws that require children to attend school until age 16.
In 2003, there was an international outcry after the European Union envoy to Romania, Baroness Emma Nicholson, demanded that a 12-year-old Roma girl and her 15-year-old common-law husband separate and cease all intimate relations until they were legally able to be married. The couple did separate for an unknown amount of time.
Jorge Sainz contributed from Madrid and Alison Mutler contributed from Bucharest, Romania.