Please, please, PLEASE! Don't make her a silly little twit who keeps getting her shapely butt into trouble every time you turn around. That will get as boring to the reader as it must be for the poor hero who has to extricate that shapely butt from its myriad perils. There is no quicker way of turning off your readers than to contrive a stupid situation into which you have the heroine thrust herself just so the hero can come galloping up at the last moment to save her. It's been done.
And done.
And done. Ad nauseum.
Found here at:
Creating Plausible, Complex Characters.
I think this should be mandatory reading for all would-be Mary Sue writers.