If she genuinely wanted to be friends again, I think she would have contacted me a long time ago.
この場合、次のような言い方ができますよ。
ーIf she genuinely wanted to be friends again, I think she would have contacted me a long time ago.
「純粋にまた友達になりたかったのなら、もうとっくに連絡してきたはずだ」
she would have ... a long time ago で「彼女はもうとっくに…してきたはずだ」と言えます。
ご参考まで!