Yours is certainly a reasonable question to ask, but it does not seem to have any support in the text. At the risk of veering off into other novels, we know from S&S and Persuasion that sisters can be--indeed, often are--very different in JA's thinking. We do not know when Darcy's mother died, although we can imagine he would at least have been as old as the difference between his own age and Georgiana's, about twelve years, so she certainly would have been around to influence him. Still, I tend to think his parents were both fine people (but then the text gives me no more direct evidence than it would give you, I admit).