Even I have trouble fighting Marie, especially with Filia. Her spammable attack don't do enough damage to make a big impact. However, you can still beat her.
Try to get in the air and spam her with all your attack while she's in her first form. Any attack should be fine, just spam until you fall, then jump again.
Use Filia's Level 1 Blockbuster (the one I introduced earlier) to chunk away at her health.
When she's in her second form, you need to play a little more defensive. Listen for Marie's audio cues (When she says ANYTHING) and just move to the opposite side of her to block her attacks. After blocking some of her attacks, go up and unleash a fury of button mashing.
When she's in her third form, she's even higher in the air then her first form. Just jump and spam moves again, it should lower her health a bit.
If you think her health is low enough, you can use Filia's Level 1 blockbuster in middair in order to chunk Marie's health by a lot.
And there she goes. Congradulations on completing Filia's story mode! Click "Next Page" to move on to the guide for Valentine's story mode.