Smother verb \ˈsmə-thər\
a : to kill (someone) by covering the face so that breathing is not possible
b : to try to keep (something) from happening : to try to stop doing (something)
“She was afraid to fall asleep; she slept with the weight of her thigh on Magda’s body; she was afraid she would smother Magda under her thigh.”
The Shawl paragraph 6
Rosa is afraid to fall asleep because she was scared the weight of her thigh might kill baby Magda.