Like Father Mateo, Marie needs an updated review now that Scarlet Keys have been released. Elle Rubash mitigates her biggest drawback—needing doom on a card to get her that extra action. Now she's fine in multiplayer as long as Elle is out since she no longer accelerates the doom clock. The only drawback is that she also needs to take Charisma to prevent Baron Samedi from bumping Elle when drawn.
At level zero, she can take Ceremonial Sickle or Dowsing Rod to get that doom. Note the Rod gives a +1 when investigating, so when put under Elle you're up to 6 before other buffs. For combat, she probably wants to upgrade to Abyssal Tome as she can just keep the doom on there while under Elle for a +2 attack (choosing whichever or is higher) and 2 damage once a turn. It exhausts so she needs a backup weapon, but she'll have her extra action for the rest of the scenario. When the doom clock resets, she can "reload" by either swinging the Tome at an enemy or use the Rod to move and investigate. With a good stat line and card pool access, plus an extra action that you can proc for the entire scenario once you're set up with no extra risk, I think Marie is finally a fun investigator to play!