Gustave has taken it upon himself to observe Marion and Sanglain following the death of the Princess and DT.   But KT thinks Gustave is in the city of Marquesas for other reasons. 
So she knew about the tail all along?
Entonces, ¿sabía que la 
observábamos desde el principio?
Entonces, ¿sabía desde el principio que les vigilábamos?
Então ela sabia o tempo todo?