When I originally read Sister Mary's Personal story I thought that it was Briliant. It Made her much better.
However I realized after coming here and reading some posts on this board my interpretation might not be correct.
My interpretation was that once activated she could re-roll one dice during the upkeep phase for ANY investigator thus protecting everyone's retainers and blessings. This is made better by the fact that 2 other people will likely get blessed to help her complete her story thus there will be a lot of protected blessed people in the game.
Other people here have voiced opinions that it only works for Sister Mary.
The problem is her "Fear No Evil" can be interpreted either way (geez this sounds familiar). All other Dice affecting abilities in the game either specifically say they work for all investigators or only the investigator who activated the ability.
A strictly literal interpretation isn't possible since one might argue that since the card says "Sister Mary may exaust" that this specifically mentions her and that only she can use it.
On the other hand it says "re-roll a die rolled during the upkeep phase" and since it just says "a die rolled" rather than "a die she rolled" that the Sister Mandy interpretation is correct.
Personally I'm going to play it for all investigators. Its probably on the same level of strength as Mandy's ability but Its delayed and Sister Mary's starting items and other ability aren't really good enough on their own to complain about over powering.
On another note I'll probably be soon posting a tier ranking of the new investigators to fulfil my need to analytically analyze and compare characters and gripe about how such and such was completly shafted (of common someone has to do it) so be looking out for it and be readyu to argue.