In chapter 29, Emma Bovary's affair with Leon is at full throttle. They have chosen a hotel room where they spend time together every Thursday, all at Emma's expense.
As part of her fantasy, Emma takes the roll of the sophisticated mistress who can afford to satisfy the whims of a younger lover. She even takes to call Leon "child" every time she asks him whether he loves her.
All of this is part of Emma's desperate attempt to reach a level of romance that can only be found in the novels that she devours at home, which inspires all of her fantasies.
One of the things that Emma lacks the most is a sincere, romantic man who would look at her with the lust that Rodolphe used to look at her, but also with the innocence that would place her above him. You may remember that Emma gave herself to Rodolphe and called him everything from her god, to her master, and her everything. Now, she knows better than to place herself beneath a man, especially after Rodolphe abandoned her so cruelly. Therefore, that look of innocence and romance "does her good" because it puts her in the role that she wants to exact in order to be in control.