Basically, I *should* be the world expert on this kind of thing - but now you're asking, I have to say, this is a bit of a poser. Certainly, I love the artifice of horror to a large extent, but I have to say, it's not a genre that the theatre has ever done that well. As a result, there aren't many obvious 'scary' plays that spring to mind. Still, my ideas for what they're worth:
a) There are a few very prominent modern 'horror' tales e.g. the adaptation of Susan Hill's The Woman in Black is fantastic (but I'm not sure it can be tweaked that easily to a female performer). As with this piece, many of the works you may find are likely to be adaptations of something that was originally literary horror - Berkoff did some interesting early adaptations of Edgar Allen Poe stories for instance, like 'Fall of the House of Usher' and there may be others. There are a couple of interesting female parts in 'The Hound of the Baskervilles', although I don't know if they have extended monologues in modern stage adaptations of the story. And so on. Writers I can think of who are likely to have had work adapated in this vein include Poe, Dickens (who wrote, especially, Christmas ghost stories), The Turn of the Screw (by Henry James - which would be brilliant, if there is a stage adaptation out there) etc.
b) The really 'big' 'horrific' genre in historical theatre was the French 'Grand Guignol' of the late 19th/early 20th century. A lot of this material is very sensationalist, sometimes truly disturbing stuff, and it's very physically nasty. Whether this provides good material for monologues, I'm less sure, although it's never less than striking stuff - the main problem with it is translations are very hard to come by, and you might even have a problem getting hold of a version of these plays via French's. However, I think there's stuff on the web you could look at, so I'd try there first, and see if you can get a feel for the genre, before shelling any money out on a book that might not be of any use.
c) It is worth considering the possibility of doing a 'vicious' historical genre that was not designed as horror per se, but has horrific components. It occurs to me that, if you're comfortable doing verse speaking, then Jacobean Revenge Tragedy is full of chilling scenes of this sort obsessed with death, morbidity and pre -meditating killing: Macbeth on crack. My great love has always been for John Webster and although 'Duchess of Malfi' is the obvious choice, 'The White Devil' has some great female speeches, too. But there's all sorts in this genre: The Changeling, Revenger's Tragedy, etc. etc. You'll probably be able to find a selection of revenge pieces placed together, and flick through them quickly to get a feel.
d) Surrealism and Romanticism don't generate scariness exactly, but in the right mood, they can provide characters/speeches which are highly unconventional and disturbing in tone. I have always felt Ibsen (Ghosts, Peer Gunt) and Strindberg (Dream Play etc.), in the right mood, conjure up this 'off - kilterness', as does Buchner (briefly) in Woyzeck, and as do a lot of the Absurdists (Ionesco especially shifts towards Grand Guignol at times in my opinion). Phillip Ridley is fantastic at doing strange things with more modern texts. Many of the characters created by these writers could be played very 'spookily' with the right choices made.
e) There are even some comic playwrights whose humour is so black that their morbidity becomes unnerving. As I've said, this is true of many Absurdists. It's also true of an old favourite of mine, Peter Barnes, who, for example, wrote Red Noses, a fantastic play which happens to be a comedy about the Black Death. You can get the same morbid/funny quality in a lot of Brecht (although whether it's Halloweeny is another question). James Saunders can be very dark as well (and every funny) if you can find his scripts still - also Joe Orton and Harold Pinter (though, I admit, they don't write as well for women as they could do).
g) One final possibility is to look for radio, rather than stage, plays - for whatever reason, horror lends itself particularly well to radio broadcast, and you may find there are more lengthy speeches in radio adaptations of work than are acceptable in the stage versions. This might provide you with the 3 minutes worth you're looking for.
Hope some of those ideas are useful.
Happy searching
Lee.
