It is believed that she is a Top Pokémon Coordinator because it has been stated:
The champion of the spring edition Pokémon Contest is Daisy Oak of Pallet Town!
Comment by Daisy
While paused for tea, I saw that you have become very strong and skillful. I hope you remain the ideal person to fight my little brother.Daisy is Blue's sister in the Pokémon games. She will give you a Town Map after obtaining the Pokédex.