I'm afraid that the name of Bastian's mother is not given in 'The Neverending Story'. It might seem a bit odd, but often in stories, not every character is fully named. Sometimes it's to keep the focus on the main characters like Bastian and his adventures in the magical world of Fantasia rather than on his family members' names. So, unfortunately, we don't know his mother's name.
I'm afraid I don't recall Bastian's mother having a specific name given in the story. It could be that the author chose not to disclose it to add an air of mystery.