I think rather than changing her mind (which to me suggests going from one extreme to another) Lizzy's negative view of Darcy is reinforced and cemented through Wickham's story. That is, Wickham provides her with information Lizzy considers as proof that Darcy is bad. And here I point to words: "I had no thought Darcy so bad as this ...", which suggests a starting point from bad and leading towards him being worse than she imagined.

So this, coupled together with Lizzy's misunderstandings regarding Darcy's motives and interest in here (and I draw on Robbin's post re Darcy's motives and his changing feelings for Lizzy, much of which Lizzy misses because of her own prejudices) suggest to me that Lizzy doesn't really understand Darcy's character or outlook.