What do we know about
When was she born? The actress is younger than Cumberbatch and Gatiss so if she's supposed to be younger why did Sherlock forget about her?
If she's supposed to be older than both boys and an arrestable age that would put Sherlock at an age that he should have remembered her.
Why was she taken away/dealt with by Mycroft? Whatever she did was very serious as Lady Smallwood knows of it too, but Mycroft was in denial she did it so it must have been surprising and seemed disputable at first.
If Mycroft could still be in contact with her if he wished to be the punishment wasn't life long.
Why does she use "Miss me?" like Moriarty were they connected or did she make the broadcast of "Miss me?" and attached Moriarty to gather extra attention?