WARNING! This trophy can be missed! You have been warned.
Marie is the Aeon Arcana, one of two new Arcana Social Links introduced with Golden. This trophy is associated with her, so here are some steps you should follow.
1) Max her Social Link as soon as possible. Using an Aeon Arcana will help with some points, as with most S.Links. Most times, she will only be able to be interacted with when she's standing outside the Velvet Room on Wednesdays, Saturdays, and Sundays after an event on 04/18. Passing from Rank 4 to 5 can only take place on or after 07/24.
2) Once you've cleared Heaven, make sure you take the path for the Normal/True Ending.
*** Spoiler - click to reveal ***Instead of persecuting Namatame, caution your team to think this through clearly. After investigating Inaba some more and asking everyone about the murders in the Spring or anyone suspicious, you and the team will rejoin in Aiya. Upon stepping outside with Naoto and Yosuke, accuse Adachi to lead the story off in the right direction.
3) After clearing Magatsu Inaba, you will have one dream during the series of events where Marie will approach you in a dream. After this has happened, head to the Velvet Room and inquire about Marie from Margaret. Persist to find her, even when she tells you it will be dangerous, rather than giving up and following her wishes to be left alone. She will call you repeatedly throughout January to inform you of her progress.
4) During the ski trip in February, you will gain access to the dungeon should everything else be met. This will be the make-or-break point, as the ski trip takes about two days (if I remember correctly). Should you and your romantic partner end up taking refuge in a cabin, this will be the trigger event for the Hollow Forest.
The Hollow Forest itself is a special dungeon. The day it becomes available to you is the same day you have to complete it, which differs from the other dungeons prior to it (where you have up to a certain point in the calendar to complete it). Along with this, each floor has specific hazards involved. For the first, fourth, and seventh floors, the enemies will be hidden and only appear when opening doors/barriers. On all floors, your SP will be halved after every fight. While in the dungeon, you're only allowed to use item/spoils obtained from it rather than from elsewhere.
The monsters are another thing. They are the toughest you have encountered thus far, and you will have two mini-bosses on your way to the end, as well as two bosses waiting for you. Go in with your best set-up as you will be here for a good bit. Completing this and getting the True Ending will also open up the Epilogue sub-story after completing the game (and available in the TV Listings after that).