80s/90s fantasy book: female protagonist, demon-related magic, "knife"/"blade" in title...?

Question

I'm trying to remember a Fantasy book I read in the late 1990s (read like it was published in the 80s or 90s) with a warrior/magic-wielding female protagonist. I think I remember looking for additional books by the author (whose name I don't remember) in in the early 2000s and it seemed like that was the only book they had written, which I found strange because it really seemed like that book launched you into a fully built out world with a complex history. I forget if this was adult or YA.

Okay so here's what I remember, and karma points if you can help! - I keep thinking there is some sort of knife/blade involved in it somehow, but I don't remember any knife beyond perhaps the first scene (described below) -- maybe blade/knife is in the title?

• Probably written in the 1990s, maybe 1980s, but it has an extremely strong and non-traditional female lead, who is pretty non-nurturing, so I'm thinking 1990s
• I don't think I was able to find more books by the author in the early 1990s -- this could have been their only one
• Classic Fantasy -- magic-wielding/warrior female lead with a subtle-lead guy who she hates but ends up marrying for an alliance, and seems to sort of fall for on their wedding night; She has a small band of friends she traveled with -- I believe there was a healer and a brawny elf?
• It wasn't that long -- about a thumb's width so 200 pages about?

• I thiiink the front cover had the woman holding a knife with some kind of evil vortex or light shining down in front of her? I believe there was some blue on the back and I remember red bits on the front, but don't quote me on that

• Not a well-known book, so forget Marion Zimmer Bradley etc.

• Starts out with the woman in some sort of academic institution that is in a stone castle or towers? She has a mind magic and wakes up from a nightmare either induced by someone else's magic or a vision from meditation of some kind
• Her magic is somehow "tainted" or has a dark side, and she is able to call up demons or something like that; she has some sort of ability to summon demons or evil and it's related to mind reading or her visions; I think her magic actually might hurt people because the "evil" guy she ends up marrying makes a big deal about their magics working well together so she can't hurt him
• I believe she has an early encounter in the academic institution with a guy who she hates (but ends of marrying at the very end because he is a prince and she is a princess, and it's a good alliance because there's a war or something) -- I think she stabs him with a knife? Maybe? There is some kind of early altercation with him I believe as a part of the vision/nightmare segment in the beginning
• This guy has some sort of evil ancestry and evil magic, and I remember him as being very pale with white hair
• She's pretty rough in her relationships with others
• She is some kind of royalty in a different land, and I believe she has a sister who took a more traditional royal role (we meet her a bit later on in the book as part of the travel/quest storyline with the main woman's band of friends)
• While in her land, or in some land during there quest there is some sort of bathing scene that involves her putting off the guy she hates and marries (trust my teenage self to remember that part but not the characters' names, jeez)
• There is a battle close to the end where the female lead has to agree to marry the guy (who is a prince) because his Dad wants an alliance with her land and and he has an army -- and there might be a part where her friend (the brawny elf man) is dying and the guy can save him so she agrees? Anyway, there's a big battle, and I believe demons are involved, or some sort of evil entity. I also think it takes place near or at the academic institution but I could be wrong about that
• One of the last parts of the book is the female lead marrying the "evil" prince who she supposedly hates, but when they marry (okay fine -- it's specifically on their wedding night) he specifically points out that their magics blend and she doesn't have to worry about hurting him. And (of course) she seems to realize he really isn't that bad and he's done a lot of great things for her, so she seems to fall for him
• Female lead is not shy about vocally sharing her disgust for the "evil" guy right to his face throughout the book

Answer 1

I think I found it! Nightseer by Laurell K Hamilton. Of course, nothing with knife or blade in it -- I have such a terrible memory, jeez. But hey, found!!

Keleios the Half-Elf was but five years old when she saw her mother murdered by the evil witch Harque. For years she has asked the gods for the strength she'll need to avenge this foul death, and it seems the gods have answered her. She's been granted an array of powers never before seen in one person, but she has also acquired a most terrifying burden, a demonmark. This mark can open the door to undreamed abilities, but it can also open her soul to the forbidden dark side of magic. Keleios must choose between the demonmark's tainted power and the lives of those she holds most dear. In an epic battle of good versus evil, of enchanted swords and shapeshifting dragons, of unquenchable hatred and unlikely love, Keleios must face her own demons—before she can acquire the most important power of all: the power to forgive.