She wrote that Christianity has "fallen into the limbo of collective ignorance.
The European Union, meanwhile, calls the omission of Christian holidays on a calendar distributed to millions of students an error.
The book was designed to act as an educational calendar for students, allowing them to write their homework and activities. At the bottom of each page, are printed inspirational quotes, information or comments for reflection.
While Christian holidays are missing, Sikh Baisakhi-Day, Yom Kippur, and the Muslim holiday Aid-el-Kebir remain listed.
"At the bottom of each page of this 'class journal' are small quotes or information devoted to various subjects and perhaps less known to European students. Some of them sometimes refer to cultural events, historical and religious...This approach led, without any deliberate intent, in the absence of references to events and important religious festivals that are very much a part of European heritage, particularly...Christmas and its importance in the Christian religion."
The EU says the Christian holidays will be put back on the calendar for future printings.