I would have never imagined that someone would describe their mother tongue as inhibiting. Maybe it's not our fault that we American's are self-centered loudmouths? ;) My wife (who's native tongue is Chinese) has related that there are some topics that she doesn't feel she can speak about clearly in Chinese. I have to wonder if the language builds cultural tools, and therefore some languages are better able to work within certain cultural situations. I've often wondered at German, and the advances in modern Philosophy and Physics that came from speakers of that language. Can German more easily handle the mesh between the abstract and the physical world? My 5mo daughter is hearing (and hopefully learning) Chinese and English everyday. I wonder if she will feel like the two languages express different sides of her personalities.
There could definitely be some truth in that! When I think about it, almost all of the "research" I have done into just about anything I can think of right now had been in English. So the vocabulary I used to think and talk about those subjects were English. Maybe it is then more difficult to discuss those same subjects in another language (Dutch for me) than in the language I usually use to think/talk about those subjects. That might also explain why there is a sense of uneasiness when using the Dutch to discuss those subjects, because I am simply not sure of how exactly to word my thoughts vocabulary-wise. Maybe this also applies to your wife when she feels she can't speak clearly about something in Chinese?