Here's what I've got so far. Feel free to add anything you think might be appropriate:
Batman, Superman, & Wonder Woman: Trinity – Matt Wagner
I showed her this as an example of a miniseries, and she took quite a shine to Matt Wagner's art. So I'm definitely going to recommend this to her, because I think she'll really like it.
Superman: Birthright – Mark Waid, Leinil Francis Yu, and Gerry Alanguilan
Pending its release as a TPB, of course. 
Superman: For All Seasons – Jeph Loeb, Tim Sale, and Bjarne Hansen
The Superman-Madman Hullabaloo! – Mike and Laura Allred
Batman: Child of Dreams – Kia Asamiya and Max Allan Collins
Easily the best Batman story I've read in years, and it does a fine job of bringing newcomers up to speed on who and what Batman is. I can't say enough great things about it.
Batman: The Long Halloween and Batman: Dark Victory (a two-volume story arc) – Jeph Loeb and Tim Sale
Batman: Black & White VOL.1 and 2 – various writers and artists
It was either this or Batman: Strange Apparitions
, and this was much more newbie-accessible. Oh, well, maybe some other time....
Kingdom Come – Mark Waid and Alex Ross
Maus – Art Spiegelman
Our college uses this as a textbook, so it shouldn't be too off-course for her. And since its violence is mostly implied rather than explicit, I don't think it'll present any problems for her.
Pedro & Me – Judd Winick
University2 and Liberty Meadows – Frank Cho
Desperate Times – Chris Eliopoulos
PvP: Player vs. Player – Scott Kurtz
The whacked-out humor and slice-of-life antics in the above three are as reader-friendly as it gets. I think she could get into these without any trouble at all.
A Distant Soil – Colleen Doran
The Chronicles of Conan (collected in three TPBs thus far) – Roy Thomas and Barry Windsor-Smith
I don't feel comfortable showing her the Busiek/Nord Conan, because of the level of graphic violence therein. But the more restrained older material might appeal to her more.
Boneyard (collected in 2 TPBs) – Richard Moore
The Sandman (collected in 11 TPBs) – Neil Gaiman and various artists
I'm undecided on this because I want to try and avoid stuff that's really complicated, but the literary references and allusions are things she'd easily sieze on. I'm on the fence regarding this one.
Strangers in Paradise (collected in 3 hardcover volumes) – Terry Moore
Bone (collected in 5 hardcover volumes) – Jeff Smith
Akiko (4 graphic novels) – Mark Crilley
Why I Hate Saturn – Kyle Baker
The Big Book of Urban Legends – various writers and artists
Some of the stuff in this is extremely funny, and she's got a warped sense of humor like me. She'd probably get a kick out of this.
Box Office Poison – Alex Robinson
The Complete Concrete – Paul Chadwick
Usagi Yojimbo (collected in at least 10 TPBs) – Stan Sakai
The Barefoot Serpent – Scott Morse
Ghost World – Daniel Clowes (this was the basis for a recent film starring Thora Birch)
American Elf: James Kochalka’s Collected Sketchbook Diaries – James Kochalka
Madman (collected in several TPBs) – Mike and Laura Allred
Promethea – Alan Moore, J.H. Williams III, and Mick Gray
Hepcats (collected in 2 TPBs) – Martin Wagner (no relation to Matt Wagner)
Stuck Rubber Baby – Howard Cruse
A Contract With God – Will Eisner
Sojourn (collected in 5 TPBs) – Ron Marz, Greg Land, and Drew Geraci
This was a last-minute addition to the list because there's such a dearth of female heroes in comics who don't look like half-naked tramps. That, and too many of the DC and Marvel heroines have too much backstory and baggage. Again, I want to keep things simple for her.
Can anyone think of something I may have overlooked?
