When Nala considered it rationally--ignoring her ingrained fear of not being fit enough to help the pride--she didn't see any harm in gaining a little weight, since Simba wanted her to and all. She wasn't enthused about the prospect of gaining, but she knew that her worries were mostly irrational, and she did want to make her mate happy. And Simba did say he only wanted her to gain a little...

The only real question was whether to tell her daughter about what she was going to do. Kiara hardly needed any more encouragement to get fat, but at the same time, she felt bad about hiding something like that from the cub.