。
She's three years older than I am.
Literal
She [topic-は] me [than-よりも] three years-older is.
The age-comparison frame ~より~年上 here uses the native counter 三つ (みっつ) instead of the Sino-Japanese counter 三歳. The native ~つ counter (ひとつ, ふたつ, みっつ...) is the catch-all when no specific counter applies, but in age expressions it carries a slightly more casual or even colloquial feel — 'three years older,' but said the way you'd discuss it casually. Beyond ten, native ~つ counting hits a wall (only 一つ through 十 とお exist), so age expressions over 10 typically switch to 歳.