It's about a girl who's run away from her family. She wants to let her mom know that she regrets going, and she loves her, but she can't come back for some reason. Maybe it's because she's been killed and she's writing from the afterlife, or maybe it's because the social have brought her off the streets, won't let her out of care.
I was writing when I just wanted to say to my mom 'I love you mom, I miss you,' but I couldn't.