Marcella

 is one of the inhabitants of Point Lookout in the year 2277.

Background
She is a Christian Missionary from the Abbey of the Road who has set up shop east of the Pier in the Disaster Relief Outpost.

Her terminal mentions describes her travel east from the Abbey to the Commonwealth. Apparently she had to leave the latter rather quickly before she had to suffer the consequences of her "doing what she could". From there, she took the Duchess Gambit south to Rivet City where she met up with Father Clifford before finally arriving at Point Lookout.

Effects of player actions
She will ask you to get The Krivbeknih, the book Obadiah Blackhall asks you to get for him, and bring it to her. If you do this she'll be found dead in her tent and in a holotape next to her corpse she'll ask you to destroy the book at the Dunwich Building. Also if asked, she will recite passages from the Bible.

Related quest: The Dark Heart of Blackhall
She opposes Obadiah Blackhall in his attempts to recover The Krivbeknih and asks the Lone Wanderer not to give the book to Blackhall. She instead asks the player to simply bring the book back to her tent, and she will take it from there. Her efforts ultimately lead to her demise. However, she leaves her last words in a holotape, begging the PC to take the book to the Dunwich Building and destroy it. She may have been killed by swampfolk thinking she had stolen the book, or Obadiah Blackhall may have hired smugglers to kill her as you will find them outside her tent when you return with the book.

Appearances
appears only in the Fallout 3 add-on Point Lookout.