Fantasy book - Female warrior blacks out & kills friends | Mage works spells like beads in mind | Shadow creature tormenting town

I remember reading this book about 15-20 years ago but for the life of my I cannot remember its name and only patches of what the book was about. I weirdly had a dream about it the other day and have been racking my brain trying to find the book!

• Classic 1980/90’s sword and sorcery book. There is an evil that must be defeated (and for the life of me I can’t remember if it was a person, thing, dark tower, big black orb etc). I think it’s maybe an evil sorcerer?

• There is a female warrior/paladin with him who’s history in the past was that she tried to defeat the big bad with a group, and she blacked out and slaughtered most of the the group before she regained consciousness. Now she’s struggling with going back again to fight it.

• The main protagonist of the book is a mage/wizard who works spells by imagining them as beads on a thread within a tapestry in his mind which was his version of a grimoire. Has to really concentrate to prepare before using any. He’s not the most charismatic of characters

• Part of the plot involves the mage/wizard being recruited to clear out a ‘curse’ on a towns well and then finds out there is some shadow/invisible big thorny evil that he has to fight which has been plaguing the town.