An attribute does not pervade every aspect of one's being. A wise man can still at times be a fool, and a smart man can make mental errors. Heiko is quite capable of exerting her charisma, I was kind of going for the whole 'uncomfortable around people, takes solace in animals' vibe.
It's like an uneducated genius, on the surface they appear deficient in their strengths, but deeper down their mental gifts shine forth.