What I am going to tell you is from my DD playing competitive soccer and wanting to play at the D1 level. She did. Different sport, but probably the same recruiting process.
College coaches get hundreds of emails from interested athletes. Just writing a coach won’t do it. Especially a head coach.
Have an honest discussion with your club coach about your skill level and ability to play at the D1 level at a SA. If he feels your skills are about the level of USMA, see if he will reach out to the coach.
Look at attending a softball summer camp at USMA and make sure your club coach reached out to the USMA coach before you attend.
See if a USMA coach will be at any of your tournaments. If so, reach out to that coach.
See about putting together a highlight reel.
The exception to this is if you are a highly recruited softball player. If you are you will know it. Top programs usually start recruiting players before the U-16 level. It’s not to say if you haven’t been recruited yet you don’t have a chance.
Finally, I would finish by saying that you should go into a D1 sport with your eyes wide open. It’s a full time job which, at a SA can really be tough, but rewarding. If you play softball at a D1 level anticipate having no life outside your team from January through the end of the school year. I knew basketball players who never got home for a Thanksgiving and missed most Christmases.
Anticipate not being home much (if at all) over the summers.
However, your teammates will probably be some of your closest friends for the rest of your life.