Answer:
I just beat Lucia and it was very difficult, just keep playing and if you're about to lose just press plus and restart, i did that many times until i won, u can hit the really cool spin shots by holding your wrist at an angle and then twisting it really fast on contact, overall it wont be that hard to beat her once you've gotten that far
I also just beat Lucia, I have been at it for about a year and managed to beat her. You have to keep at it and even when the score is 1 to you and maybe 4 to her keep playing on. She does tend to make mistakes such as hit the ball out and miss your balls sometimes. You should also play an 11 score match. To do this when screen which has the player selection on before you press 'OK' hold down 2 and keep it held until you reach the page where the screen shows who you are playing. Then when you start to play you will see at the top that instead of a 6 point match it is a 11 point match. Also try not to make silly mistakes because it could be going really well and then you make a silly mistake and it could be over. Also restart your game if Lucia has won. Try to also hit fast shots at the opposite angle to where she is and keep doing it and eventually it will catch her out. These are the techniques that I used to defeat her, but remember just to have fun. :)