The very first sentence: radiant figure but cast no shadows, suggests that something about her is lacking. Also, if you read further, "spoiling her with injudicious petting of her limitations" corroborates the idea. So the first blank should be missing.

Basically the sentence is saying that she was bright but didn't create any major or noticeable impact, she was treated like a child as in she was spoiled and pampered despite her limitations. No one raised any objections to her weaknesses. She was so good and had a strong persona that made people to ignore all her peccadilloes.

Therefore, to encourage her as you would normally do to a child, you would actually indulge their tricks. so indulging should make sense.

For the third blank, only brisk fits, as desultory means careless and surly means ill tempered.