。
She shuddered in fear.
Literal
She [topic-は] terrible-(causal-て) body-trembled.
Two pieces of i-adjective grammar. 恐ろしくて is the te-form of 恐ろしい — used here in its causal sense ('because terrifying'). The same construction works for any i-adjective: 寒くて震える ('tremble because it's cold'), 嬉しくて泣く ('cry from happiness'). 身震い ('shudder, full-body tremble') is built from 身 ('body') + 震い (the masu-stem of 震える) — the compound emphasizes a whole-body shudder rather than a smaller tremor.