This is easier than it sounds. Simply kick her stars out of the air. You can do this by waiting against the back of the screen and using a mid-kick, jump-kick, or low-kick to hit the stars since only throws them high, mid, or low.
Hold the kick button
down and press in the proper direction to perform a kick to hit the stars:
for a jump kick and
for a low kick. I also suggest using the d-pad since it is easier to hit the correct direction than a thumbstick (at least for me).
You can also jump over the stars if you can't hit them. She will start by throwing one, then throw two in a row after a few seconds. If you connect, you will get a red star (just like when you hit a fighter), if it hits you, there will be a black star and a loss of one health bar. You have eight health bars to do this, and should have an extra life after the first fight to try again.
(Let me know if anything is unclear instead of neg-voting and I will edit this as needed)