I don't think anybody doubts how nice and loyal Tatiana is, she's been part of the Casiraghi's group for quite a while, even before dating Andrea, and looking at how private they are, I imagine they wouldn't just welcome anybody.
My biggest irritation with her is that she looks so miserable and awkward in all the pictures, you say maybe she doesn't photograph well but I've seen the odd photo where she's actually smiling and she looks beautiful, if she feels awkward with the situation at an event (she's just there supporting a friend/Andrea,etc) she can always decline to be photographed (in most events that she attends they do ask people permission to take their photo)instead of looking bored and irritated at being there, I know in candids is impossible but still...
as for her style, it's not my cup of tea but I don't think with her friends and her fashion knowledge (she does attend the shows) that she's oblivious to what's going on, she chooses to wear what she does without any help (im sure she's beeen offered plenty) so more power to her for wearing whatever she wants and not letting other people's opinion get in the way.