"... her heart revelled in angry pleasure, in pleased contempt"

Those are very strong emotions Lady Russell is experiencing here. I wonder why.

I've no doubt she was highly gratified by her success at bringing about the end of the engagement, but she loves Anne and sincerely wants the best for her. LR is a rational woman of sound abilities, and it cannot have escaped her notice that the outcome for Anne was six years of misery and spinsterhood, which I don't think was what she wanted for Anne at all.

Did LR experience any moments of self-doubt when she saw the long-term results of her actions, and feel that she was in some measure to blame for Anne's unhappiness and loneliness? If so, the strength of her feelings when her judgement seems to be proved right could in part reflect her relief
that she need no longer feel herself blameable.

Or maybe her anger and contempt reflect the depths of her personal dislike of Captain W.

But perhaps she simply "revels" in the pleasure of being proved right because she cares more about that than about Anne's unhappiness - a rather ugly picture of LR.