Charisma is not appearance. It is a force of personality and the drive behind any good Politician. I just found it somewhat amusing that such a high ranking charisma persona would have any trace of shyness in her.
I should note that there are certain settings in which Heiko is comfortable and can actually apply that 20 charisma. For example, formal dinners. Again, she did go to charm school, so in situations where she could apply it, she can be quite persuasive and composed.