This question contains spoilers…
(view spoiler)[When you cast the runes for Rhiannon did you actually change the course of the story slightly in accordance with what they showed, or do you suspect you might have read them the way you wanted to fit the plot you already had mapped out to its conclusion? (hide spoiler)]
It was a bit of both. Mostly, the rune castings fitted the indecisions, maybe that's not the right word, doubts Rhiannon had in her mind and the outside influences the plot was bringing, unknown to her, to her doorstep. Her main question was what should she do about Alana? As Rhiannon herself says, runes are personal to the caster and he/she reads them in a way that makes sense to him/her or throws light on a particular problem: a way of crystalising certain things that need resolution. The castings did largely fit what I had in mind, but also pointed the way to the things Rhiannon did, so yes, they change the plot to some extent, in fact, thinking about it they changed it quite a lot. I certainly noticed a difference when I allowed the runes to 'speak for themselves' and did real castings; the novel took on a life of its own.