。
She is as tall as I am.
Literal
She [topic-は] me [as-と] same-amount stature [subject-が] tall.
背が高い is the idiomatic way to say 'tall' (literally 'the back/stature is high') — Japanese describes height through a body-part subject (背) rather than a single adjective applied to the person. The same pattern appears in 目が大きい ('eyes are big' = 'has big eyes') and 頭がいい ('head is good' = 'is smart'). Combine that with と同じくらい for an equal comparison and you get 'her stature is tall to the same extent as mine.'