Arwen is the best hero in the game for getting max score, as there isn't a lot of healing in the game at the moment. Her 3 willpower powers fates and her heal is worth 12-18 healing per game. Without her, it's challenging to have your guys healthy enough at the end of game to get the max score on health.
Upkeep: Restore 1 [health] to 1 Character
—The Fellowship of the Ring
Core Set #2. Lore.
At the moment, as of 9/11/2018, Arwen feels indispensable for getting max score. I'm not saying its impossible, but I think her healing, plus her 3 makes her perfect for the job. She feels like the digital equivalent of spirit Glorfindel.
Now, at current difficulty, I'm not sure that that is a bad thing. Her innate ability allows 275 on hard to feel possible. I've taken Éowyn merely for her 3 , and she offers that with a bonus. At the moment, I think there is no doubt that she is the strongest hero in the game.