Yup. My daughter was in your spot 2 years ago when she first expressed interest in USNA. I our case it was DD and I vs. Mom the entire extended family. We are not a military family.
Short hand advice:
1) Ask your Mom how long she intends/thinks she can to exercise this kind of control over you, AND does she really want to control what information you are allowed to have?---(bet you get tons of comments along this line--stand by)
2) Be respectful of any concerns she has about your safety---then remind her that most USN Officers are not F18 Pilots, Seals, or Forest Recon. Can she recall a DDG, LHS, Carrier being sunk? If that where to happend we are all "knee deep" anyway
3) Tell her that IF you attend the USNA you have no service obligation unless you sign a service commitment at THE END of YOUR SECOND YEAR.
All the way up to plebe parent weekend my wife would tell her horrified relatives that DD could attend USNA for two years, attain majority, leave and finish at Oxford (she had Cambridge A and O levels done).
4) If it’s a political thing, remind her that your oath is to defend the (exceptional) Constitution of this country, not a political party, President etc.
5)Have a look at the USNA course requirements, (this was a big thing for me) There are no 'Tree House Design', 'Basket Weaving' or freshmen level 'International Joint Ventures' classes. If you go to a service academy your first to years take you somewhere in terms of useable knowledge and building blocks for advanced study, you won't be flopping around taking "Fun Classes".
6) Follow up #5 with a FORCEFUL statement that you want an undergrad degree that means something, (lots of info around on the *#*p that passes for a BA, BS these days
7) If your Dad has some business contacts see if you can get a 3rd party to explain to your Mom the tremendous respect the private sector has for USNA grads. (BTW it shows up in salaries)----- I did this with my wife. If I'd said it---"meh"; somebody else saying it really got her attention
8) Sit down with dad, get a pencil and work through the numbers. Assuming you aren't a candidate for big time financial aid, costs to send you anywhere but the local public university will run between $55K and $75K a year or around $300K. -----then off to grad school??? (no student aid for that). At USNA you are paid to go to school--and you land a fairly well paying (inc benefits pkg) when you join the fleet. If, at the end of 5 years, you find that you "have a fever the only prescription is more NAVY"... great. If not, you have money saved up for grad school, and Dad still has some cash around, you saved him $300K after all; (I hear that from my DD now and then). Then there's that GI bill.
9)Following up on #8 (and my favorite) is this. If you decide to leave the Navy after 5 years (first re-up gate) you will have other decisions to make. What to you want to study at a grad level? what work do you want to do? where do you want to live? If you go USNA you make these decisions at 26-27 AFTER seeing some of the world, doing work that employers, universities respect and getting to know yourself as an adult. Go the standard route and by the time you are 23 you will be invested in a career path that probably has its beginnings in classes took and decisions that you made at 19 or 20. PERSONALLY I THINK THIS IS HUGE.
10) Google USNA class of 2020 and down-load the breakdown of the USNA CL of 2020, show it to Mom. It’s a pretty impressive group to go to class with, live with and have as life-long "been through it together buddies".
11) NOTE that best case for the USNA is a 5 min conversation with a Mid; the second best is a 15 min conversation with a Mid's parent. If you can get your Mom to the YARD to see the place, to meet some Mids---- YOU WIN! .
The night my kid pulled the trigger on her appointment, I asked her to tell me "why Navy",(her Mom wasn't home at the time and I was covering my own @@@). She said "Dad I've done recruiting visits all over the country and honestly I can't remember much about any of the kids I met, (they all kinda melt together). Navy was different, every Mid I met on my recruiting trip was engaged, interested, and interesting. I wanted to know more about each of them; that’s why.
3 months later my wife went to I-Day at USNA. It wasn't an easy trip for her, but she left immensely proud of DD and proud to be a Navy Mom, (that sentiment as only grown over time).
Hope something here has value for you----good luck!