Translation:The woman who is coming is my mother.
The woman who is coming is my mother, in written English this is more correct. It was marked wrong. The person who translated the phrases from Greek has a real problem with the apostrophe. In written English it should only be used to denote possession, in spoken English the i in is, can be elided she's. The big exception in written English is "It's", " it's sunny" When it denotes possession it does not have an apostrophe, " the stable is famous, its horses run in the Derby".