現在完了形

「have」は間違いです。主語が三人称単数ですから。

My older sister is going to Australia to study English.
My older sister is in Australia to study English.
My older sister has been to Australia to study English.
My two sisters have been to Australia to study English.
My older sister has gone to Australia to study English.
My older sister had been to Australia to study English.
My older sister had gone to Australia to study English.
please put into these sentences into GT.
I suppose you can get the difference of the meaning.

:GT.
https://translate.google.co.jp/?hl=ja&sl=en&tl=ja&op=translate