I sitll would not say "cruel".. I think that at first she does not know Fanny all that well, and has lukewarm feelings for her...and is accustomed to Henry's game with girls.. but thinks that the fashionable young ladies he plays with have "few affections worht bothtering about" so she thinks that Fanny will possibly suffer a little if she falls for Henry but its not that terrible. She's indifferent rahter than cruel.

As for her reactions towards Maria, again I think she is being catty but not necessarily cruel. I think that perhaps it would be correct to say that she gets a mild pleasure out of "getting a reaction" out of someone, but she does not set out deliberately to hurt people....
I think taht she has a poor opinion of people in general and again thinks that Maria is not that worthy a character and if she suffers a bit over Henrys dropping her and taking up Fanny, its nto that bad Again I suppose she feels that Maria's feelings for Henry are mostly to do with lust and pride, nad that she was willing to marry Rushworth for his money, so why should she expect to be treated as if her feelings were very storng or of great account...