You have to let her help you three times in order to finish her sidequest and get the Last Breath trophy as well as prayer for Firm Devotion. Viridiana: Viridiana is an NPC that offers to help you during certain boss fights.
See Mediterranean Diet for more information.
There are a lot of missable trophies due to the fact that you can reach cut-off points for some of the sidequests and thus won't be rewarded with upgrades that allow you to reach certain other places/get yet other items which are tied to more trophies. Trophy-wise the game has your typical array for this type of game: Beat all bosses, get all the collectables, complete all sidequests and do a short speedrun. Fight your way through the abominations the inhabitants of this land have become and find true salvation in penance.
Do you like Dark Souls? Can't get enough of Metroidvania's? Ever wondered what would happen if you transported Hollow Knight into a world ravaged by religious blasphemy, living out its version of the Spanish Inquisiton? Then you have come to the right place! The story follows our hero, The Penitent One, as he travels through the land of Custodia, which has been ravaged for centuries by The Miracle, a mysterious, supernatural entity, manifesting itself in blessings and curses upon the people of the land.