Michael has totally overbought for Nikita. I'm sure the dress, shoes and coat are just the tip of the iceberg for what Michael has gotten her. And she already thinks that he has given her too much.
All she got for him, which is perfect, is the medallion of St. Michael. So she is going to be embarrassed that he has gotten so much for her. And she is already hugely uncomfortable that he has made such a fancy dinner and now wants her to go to Christmas Eve Mass. The poor girl has never even been to church in her whole life.
I just get the feeling that he is totally overwhelming her right now but she won't dream os telling him that and dissappointing him on Christmas.