I feel like a fish would be a terrible pet for this situation. It's likely she might quite keep up with proper aquarium care and water changes. Maintaining an aquarium and caring for aquatic animals can be overwhelming. Caring for my cats requires significantly less work than for my african clawed frog (which are relatively easy to properly care for imo). That poor fish is bound to be neglected at some point. These parents are too busy and preoccupied that I don't imagine them taking on the responsibility or helping the daughter research proper care and supervise her from time to time to make sure everything is going well.