How can my daughter increase her chances of service academy selection? Which one is best for cyber?

For myself, HS grades were a factor, but less important than SAT/ACT scores. Those scores are probably the single largest factor in a large number of factors. But the "whole person" concept is still huge at USAFA, so involvement, success, and leadership in sports and other extracurricular activities (from Scouting to band to employment to community service) are all important factors. If your daughter is an athlete, especially if she has won at the conference/district/state level, reach out to the USAFA coach of that sport. I was surprised to learn (after the fact) that a single note from the men's gymnastics coach made my application folder different enough. So it doesn't need to be a big sport to help, but if it is (basketball, softball, soccer) even better. BTW, my dad watched boilers in a paper plant for a living...so while I'm sure it never hurts to have a senator as your uncle, it is not a requirement.

As far as cyber goes, the USAF seems to be positioning to take the lead in that area.
In order to get into the service academies, there are many routes. She will need to build a resume of academic, community, and athletic achievement. Joining groups like National Honor Society looks good.
Once she has that together, getting a Congressman to sponsor her is the surest route. Volunteering to be a paige or intern in their office opens doors and access.

Most Congress people have web sites that address their individual processes and minimum standards for considering a high school student for an appointment. Also, the Service Academies have information available, probably on their web site, about appointments, minimum admission standards, and processes. High School guidance counselors may have information from the Academies or Congress members also.

I tried for an appointment in the 1960s and I suspect that things haven't changed all that much. It helps a lot if you or somebody you know well is a friend of the Congress person to whom she will address her request. (My grandfather knew the Representative to whom I applied.) Very high SAT scores will help a lot (I had average SAT) as will being a straight-A high school student (I was more of a straight-B student). A record of both athletic and social leadership will help her too (I bombed on this one because I wasn't a jock at all). I took ROTC in college.

Look into Vice Presidential appointments also. I need to look it up, but I think she might be eligible for VP consideration because you are a vet.