Catherine's first thoughts of Thorpe appear mixed.
His manners towards his mother & sisters did not please her 'but he was James's friend and Isabella's brother.'
I think she was flattered by the compliment rather than John himself.
I notice it is wonderful Isabella who tells her, not John himself.
Catherine does tell James when he asks, that she finds John 'agreeable' but she felt under pressure by James and Isabella.
Her head briefly turned maybe, but she would have answered she did not like him at all had there been no friendship or flattery in the case.