keep Mr Collins happy. And I think she will be busy. But I have concerns that she will continue to be content w/ such a fool of a husband. When the other adult in the house is not someone with whom she can have a rational conversation, not someone with whom she can reach rational decisions regarding their children, then I think Charlotte's life will become more and more empty -- especially if her children inherit their father's intellectual capacity rather than their mother's.

As for security, much of that depends on: how soon Mr Bennet dies AND whether Mr Collins survives Mr Bennet. If Mr Collins were to dies within a few years, and Mr Bennet were still alive at that time, then Charlotte would be back at Lucas Lodge, a dependent widow (possibly with a few children). This may not be the likeliest scenario, but it is certainly a possibility. There is no indication that Mr Collins has much (if any) independent fortune, so Charlotte could still be a burden on her family -- a bigger burden, actually, if she has children.