The issue was not mentors in general. It was mentors in STEM fields.
Single female parents, female elementary school teachers, female girl scout leaders, female atheletic coaches (typically in female associated atheletics such as gymnastics, dance and cheerleading) etc. can be excellent positive same-sex role models in many areas. But in the vast majority of circumstances they are not and cannot be positive same-sex STEM mentors/role models by virtue of the fact that they are typically not themselves involved in STEM careers, nor in many cases do they even know someone who would be a positive same-sex STEM mentor for a young girl.
Boys are much more likely to have male parents, male scout leaders, male coaches, male teachers etc. who may function as positive same-sex role models in those particular areas, but who are much more likely to fill the role of same-sex STEM mentors/role models, again by virtue of the fact that they themselves are more likely to be involved in or know someone involved in a STEM career who could mentor a young boy.
Regardless of whether and/or how the industries are 'designed' (for lack of a better word), boys get bombarded with the message that they are welcome, simply by the sheer number of places that they observe male role models in those STEM fields - whether it be that 6 out of 7 crew members on a shuttle mission are men, that teachers of STEM subjects in secondary education and above are vastly dominated by males, or by the depictions in pop culture, from Phineas and Ferb to Big Bang Theory. The message girls get is that they are not welcome.
My question is why aren't you equally outraged by the message your DD is getting in nearly every exposure she has to STEM fields. That message is insidious and it's pervasive and it's abundantly clear that females (including her) are generally not included or welcome in those fields. Here is a chance to counterbalance that message and it doesn't take anything away from the boys - they still get the message that they are welcome from every other venue in the STEM fields.
Do you agree that it is valuable for a young girl interested in STEM to have a STEM mentor of the same gender? What other suggestions do you have to figure out how to connect this rare resource of female STEM mentors with young girls?
Should this rare and unique resource be monopolized by large numbers of boys, who have other STEM resources, to the point where access by girls is effectively swamped based on sheer numbers? That's what happens in many other places, only a few of which have been mentioned by other posters on this thread.
It's not really fair to object and tear down these types of programs without considering how to achieve the goal without the parts you find objectionable. If your objection is that you really don't believe that same-sex STEM mentors are valuable, particularly for girls, then nothing else I say will matter.
If you are concerned that your DS will get the wrong message from this program, NASA has other mentor programs that have no reference to gender and both your children would be welcome there. My guess is that most of those programs, though, are dominated by men and your DD may not find a mentor there, while your son most likely would.
