She is just being used by him for his convenience.
He just takes what he wants from her without thinking of her needs.
この場合、次のような言い方ができますよ。
ーShe is just being used by him for his convenience.
「彼女は彼の都合の良いように使われている」=「彼女は彼にとって都合の良い存在だ」
ーHe just takes what he wants from her without thinking of her needs.
「彼は彼女のニーズを考えず、彼女から欲しいものを取るだけだ」=「彼女は彼にとって都合の良い存在だ」
ご参考まで!