Should crowd her down in the slippery street.
Line 17: "Lest the carriage wheels or the horses’ feet"
Line 18: "Should crowd her down in the slippery street."
" Lest the carriage wheels or the horses’ feet "
(She is afraid that carriage wheels or horses may hit her.)
" Should crowd her down in the slippery street. "
(She fears being knocked down on the slippery road.)
Overall meaning: She fears the carriage wheels, horses and slippery road.