A Disney princess is someone you (should) long to be like for your whole life (forever).
A Disney princess is someone girls admire for their whole lives.
「ディズニープリンセスはあなたにとって永遠の憧れのはずです」= A Disney princess is someone you (should) long to be like for your whole life (forever). / A Disney princess is someone girls admire for their whole lives.
文脈とニュアンスは分かりませんが、日本語を直訳すると上記の英語になります。
ボキャブラリー
someone = だれか、人
should = ~なはず
long to be like, admire = 憧れる
whole life, forever = 永遠
girls = 女の子