I dreamt about Monique last night. We were standing together on a beach in a sunset. I kept trying to talk to her. She was silent for a long time, and then she said to me, 'Adena, hear me. Tomorrow is another day. Another day, another destiny.'

Does anyone have any idea at all what this could mean? I know it's possible to see ghosts in your dreams, but was this actually a ghost?

Probably not a ghost, but more of your subconscieuos(spelling suck) thinking about her.
If you ask my daughter, it was a ghost, I just don't how much I believe in that.
You are wanting to see your friend, and your mind does it in your dreams! Aren't dreams ;lovely sometimes?
It sounds like you know that your life is going to go on and with her telling you that, perhaps you are confirming what you already know?
IDK
((((((((((((((((((((HUGS)))))))))))))))))))))))