。
She showed up before long.
Literal
She [topic-は] before-long arrived.
ほどなく is a literary/written adverb meaning 'before long, soon thereafter' — built from 程 ('extent, degree') + 無く ('without'), literally 'with no extent (of time) passing.' It carries a slightly elevated tone, common in narration. やってくる is a compound verb (やる + くる) meaning 'come about, arrive, show up' — 'to materialize on the scene.' The pair gives a quietly literary 'before long, she made her appearance' feel.