I sent a message to a friend that’s been locked up for awhile, she hasn’t responded and I don’t know if she even got my message, I’m not sure how to contact or reach out next?

All you can do is continue writing letters. Some inmates, especially newly incarcerated ones are affected by the harsh disconnection from society. They might be "in their feelings" and are not ready to communicate with people on the outside just yet.  If you are persistent, the letters will eventually make an impact and she will eventually respond.