Charlotte does have a quite strong sense of self -interest/preservation.

I think it was tha timpluse that induced her to marry Mr Collins in the first instance: and I agree with Lizzy that viewed in the light of prudence its a good match for her.

I think she is very aware of the possibilities for preferment and is crucially keen to promote connections, for that is how the early 19th century world worked. It would have been out of character not to keep all her financial options open ;-)