Hmm...must have rolled over onto her back at some point, and the shoulder strap had fallen off. Or maybe she had just kicked off the covers showing her panties.

Is that enough of Alice's blood to tag the image with Alice?

How to kill a magician- Marisa's way

im guessing:
Alice climbed up to see if Marisa was home, saw Marisa was sleeping in her underwear, and upon seeing her, gained a nosebleed that shot out enough force to propell her off the window and onto the ground, leaving a crater.