Yes. From 1866-1929, Italy only recognized civil marriage for legal purposes. The Catholic Church didn't like that (and also didn't like that they lost all their territory in the Papal States as well as Rome to the new Italian Kingdom) and instructed the faithful not to participate in civil marriage. So, many Italian couples would have a church marriage but not a civil marriage. Their children would be legitimate in the eyes of the church but not for legal purposes. But it was still considered shameful to be named as the mother of an illegitimate child, and because Italian law gave the parent of an illegitimate child the option of remaining anonymous, many did. In some instances, the father would register the birth and the mother would be un-named. In other instances both parents would remain anonymous and the child would be registered as a foundling and assigned a different surname. In some rare instances the mother would register the child and the father would refuse to be named.
But having children that were illegitimate in the eyes of the law caused problems - they could not legally inherit property, and if they survived to adulthood and were to marry, they would be listed as illegitimate on their marriage record. So most Italian couples eventually would have a civil marriage and legitimize their children retroactively. This would be noted on the marriage record along with the names of the children and their dates of registration.
In the case of this child, her parents were not legally married when she was born nor when she died, so officially, her mother was unknown. Deceased illegitimate children were not legitimized when their parents eventually married in a civil ceremony.
BTW, the phrase is "madre ignota".
