The Women's Sports Foundation recently published* 2006-07 data showing for each state the percentage of high school athletic opportunities offered to girls. WSF then ranked each state by the difference between the percentage of athletic opportunity for girls and the percentage of female students overall.
By this measure, the number one state for female high school athletes is ... New Hampshire! New Hampshire girls receive 47.1% of high school athletic opportunities and make up 49% of the student population, giving it the highest score of any state, -1.9. Pennsylvania was a close second place, with a score of -2. Maine, Vermont, and Minnesota rounded out the top five (all > -3).
Alabama, whose high schools only offer 32.3% of athletic opportunities to girls, has the worst score of any state, -17. Louisiana, D.C., Tennessee, and South Carolina round out the bottom of the list, with scores ranging from -15.9 to -12.5.
*a temporary "homemade" link is provided here, which I will replace with an official, permanent WSF link once the data summary is posted on its website.