Melissa, its not the jawline that's the marker, its the chin, the height and shape of the chin is VERY important.
Many many many women have quite large jawlines with angles that are not open, as long as the chin is small and rounded it doesn't matter.
Check out Molly Sims (Vegas) Jawline, very masculine from the front, and side, but she has a very cute female chin. Emily Deschanel (Bones) has an incredibly wide jaw with a jaw angle almost 90%, yet nobody would say she's a man because of her chin.
I've got frontal photos, not the usual from the top photos, which reduces jaw width of a lot of actresses/models who have wide squarish jaws with small rounded chins: angelina Jolie, Ashley Judd, Audrey Tautou, Catherine Zeta Jones, Rebecca Romjin (She's doing a TS on Ugly Betty), Katherine Heigl (Grey's Anatomy), Mischa Barton (OC), Gwyneth Paltrow, Diane Kruger, Jordana Brewster, Keira Knightley, Maria Menounos (Anchor), Paris Hilton, Jennifer Connely, Rachel Leigh Cook, Sophia Bush, Eva Herzigova (SuperModel), Gisele Bundchen (SuperModel), Shalom Harlow (Actress/SuperModel), Kate Bosworth (Actress), Grace Kelly, Selma Blair, Heidi Klum, Claudia Schiffer, Amanda Peet (Actress), Kristin Davis (Sex and the City), Kristin Kreuk (SuperModel), Laetitia Casta (SuperModel/Actress), Alison Lohman (Actress), Kristen Bell (Veronica Mars), Ornella Muti (Bollywood Actress), Renee Zellweger, Hillary Swank (there's a reason she did boys don't cry), etc.
Obviously, if you have a small chin, you jawline will look less imposing even if its wide and the angle is acute.