Final answer:
Adeline is described positively in the passage, suggesting that she retains a lively and attractive energy; therefore, 'happier' and 'brighter' are the most fitting words to complete the sentence about her growing older and taller.
Step-by-step explanation:
Adeline is described as having lost none of her vivacity and her blue eyes still retain their melting quality. Although the passage does not directly discuss her physical appearance in the context of becoming prettier or slimmer, it does suggest that she has matured and still possesses a lively and attractive energy. Given the context and the positive connotation of the words, the best fit for the blanks in the sentence would be "Adeline is looking happier, and brighter as she grows older and taller."