We should probably ask what Ranald would prefer here. Does it serve him best for Mathild to take on the role as local leader of the Cult of Ranald? He has many other priests who could do that.
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If Mathilde wants to claim the temple of an evil god, even if someone else was foolish enough to occupy it, even a hint should be enough to get it, and not just to curry favour, but when a wizard tells you to move out of a place like that, you don't ask for a second, you move. Adventurers in Warhammer may have their own brand of recklessness, but any surviving ones will be appropriately afraid of the dangers mysterious evil magic.
Althoughter, this ,eans that claiming the temple can be put pretty much at the end of the priority list. We'll probably want to get to it in a couple of years, after a priest of Ranald who can actually run the place and cast the divine ritual required to actually consecrate the place drifts in, but at the moment Mathilde is to busy to establish it,much too busy for the full time job of tending to a congregation, and can't even perform the divine magic required to actually turn it into a real temple. It shouldn't be considered on the same type of list as the options that have actual urgency.