、。
She's good at speaking English — every bit as good as her older brother.
Literal
She [topic-は] English [object-を] speaking [subject-が] skilled [copula-で], older-brother [to-に] surpassing [even-とも] inferior-not extent [copula-だ].
勝るとも劣らぬ (まさるともおとらぬ, 'rivaling if not surpassing') is a classical set phrase used here to back up the praise — 'her English equals or exceeds her brother's.' The sentence presents the skill first (英語を話すのが得意 — 'good at speaking English'), then appends the comparison via で-form chaining, a measured rhythm typical of evaluative observation.