I know in a human, subcutaneous emphysema can occur for multiple reasons. But, I have no idea in snakes. Has she shed? Is she bloated? What color is her belly?
You won't hear SCE in humans with an unaided ear. It's something you feel under the skin.
If OP can audibly hear & feel cracks, I'm willing to bet it does have something to do with her ribs and/or spine.
How is she acting? Is she lethargic? Does she flick her tongue?