The Tenant of 221C

This is a fan-fiction of Sherlock, the BBC series. The protagonist comes into the picture after John married Mary and left. Just in case you encounter spoilers :D.

Synopsis:
She used to be only a pass by, but decided to stay in England for Mrs. Hudson.
She used to be only a spectator, now she has no choice but to accept the invitation.
She was forced, but now making a willing move for the sake of Mary.
She used to be unimportant, but for Mycroft, she had no choice but to become the main character.
About John, he was the start of all this chaos. Without him, nothing would have happened. It was all his fault.
What should she do now?