Personally speaking, I like to make curry with chicken- especially chicken thigh. And I prefer turnip to potato, it doesn't dissolve into the broth. These things are a matter of personal taste!
(Also, I think since Kiyo is a cook, she's almost certainly getting a salary. It just is probably being paid into an account for her. Giving her 'pocket money' is probably the mother of the house giving her a bonus to have a nice day off with, so she doesn't have to spend her own money on like, food for the day.)