Well almost all of fans said that the reason why she didn't tell the BO about Shinichi and Shiho condition is to protect them but after re-read the conversation between Yukiko and Vermouth in the Mystery train case. i found something intriguing about the last moment of the conversation.
When Yukiko asked vermouth if the software made by suguru itakura was the reason behind vermouth kept about shinichi condition a secret. She didn't say anything and end their conversation quickly.
Then what is the significance of it? Well... If you look at all of important conversation between two character which end up with unanswered question like jodie and vermouth, sera and conan, etc. i think that was Gosho's way of telling clue to fans.
And what does it mean?
it means that somehow wanted to protect something else beside conan by not telling their condition, but something was not match up... first the request of that software is 2 years ago and vermouth contacted suguru around one years ago before shinichi shrunken. Then does it mean it would be bad for her (not only for shinichi sake but for her too) if BO found the fact that shinichi was shrunken.
well i have two made up reason to explain her reason..
1. She have an important person for her shrunken, but you can say it may support one of theory about anokata too. well i'm not sure about this theory and i'm one of the people who doesn't believe it. but if BO boss is someone important to her then the theory about "anokata was shrunken to child body and she was the one who kept it secret" become possible
2. The one thing that kept her from doing BO's order because that important person (either it is the boss or another people) .... Isn't she said that only two poeple she loved most in the world which one of them is ran, and i dont think the other one is shinichi.
oh another made up reason
the reason she hate shiho and her parent so much can be explained by this made up theory. the cause is 2 point that i stated before.
Ok this is my theory, and like i said it is only made up theory.
Still it's possible to be true right? Wahahaha...
It seems there are many fans who have same thought... and this is just a common/old theory after all .
So i will add up every speculation in my mind about vermouth and change the title little bit (i hope it doesn't break any rule).
I will update it soon