It seems that Miranda didn't write a diary entry for June 9, but instead, she made a note of a poem that Bethany had read to her. She mentions that the dark nature of the poem makes her worried about Bethany's mental health, and she transcribed the words.
I'm not gonna lie. It's... it's a strange poem.
Heaven is on the Ocean's Floor,
So do not fear, step through the door.
And you will hurt and think no more
Of that so quiet time before.
Through the waves, away from the shore,
Let your blood be blood no more.