She run her mouth, but can't eat right
from Malik Yusef (Ft. CyHi Da Prince, John Legend, Teyana Taylor & Travis Scott) – Sin City Lyrics on Rap Genius
Meaning
This should go hand-in-hand with the line next to this one, saying that although his girl will gossip and bitch, i.e. ‘running her mouth,’ she can’t eat correctly, or use her mouth in one of its two useful functions. Whether this is due to anorexia, or due to cocaine causing a loss of appetite, is not specified.
Here’s a moderately skinny model.

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