。
She's the same height as you.
Literal
She [topic-は] you [as-と] same back's-height is.
Japanese describes height as 背の高さ ('the height of one's back') — 背 means 'back/spine' and serves as the standard reference point for body height. The pattern XはYと同じZだ ('X is the same Z as Y') marks the standard of comparison with と and the dimension of comparison with 同じ + noun. Note that 背が高い ('back is tall') is the everyday adjectival expression for being tall — Japanese builds many of its height/size expressions around 背.