Info on the Mercury 13
Here is a link on the people who should have been sent up with or instead of John Glenn.
The Mercury 13 were the female portion of the Mercury program.
The lack of any female astronauts in actual Mercury capsules is an indicator of why this is an issue.
This isn't my area of concern usually, but these women got screwed, they met all requirements and were perfectly capable. Some were aviation pioneers in their own right.
A few are still alive and have stayed healthy. If they could send Glenn into space they can certainly send some of these ladies into space.