high expectations = 理想が高い
unrealistic standards = 非現実的な基準
質問者さんが表現したいのは:
I have a friend who can't get married because she has high expectations = わたしの女友達で理想が高くて結婚出来ない子が居る
と言いましょう。アドバイスする場合は:
You should lower your standards if you want to get married = 結婚をしたいなら理想を下げるべきだよ