There also might have been some other typo. Or Duo does not have its day. That said though. In a short sentence like this when you are saying about yourself that you are this or that (katerina, teacher) you would actually use the personal pronoun in most cases. Not sure if it is because of the use of TO BE or because such sentences typically begin the conversation but to say just "jsem katerina" or "jsem ucitelka" is very unusual. Not wrong, just not typical.