。
She has long legs.
Literal
She [topic-は] long legs is.
長い足だ ('is long legs') is an unusual predication structure — it describes the whole person by a single attribute. This is a colloquial shorthand; the more grammatically complete version would be 足が長い ('her legs are long') or 長い足をしている ('she has long legs'). The compressed form sounds direct and observational.