"She has a propensity for anxiety and she never had a day where she felt at ease."
"She has a tendency to be anxious ~"
"She has a propensity for anxiety and she never had a day where she felt at ease."
"She has ~" 「彼女は〜があり」
"a propensity for~" 「〜の傾向」
"anxiety" 「心配性」
"she never had a day where ~" 「〜日はなかった」
"where she felt at ease" 「気が休まる」
"She has a tendency to be anxious ~"
"a tendency ~" 「〜傾向があり」
"to be anxious" 「心配する」
She has a strong propensity towards anxiety which means she never gets a day off from her worries.
この場合、propensity for anxiety ではなく、propensity towards anxiety と言ったほうが自然ですよ。
ーShe has a strong propensity towards anxiety which means she never gets a day off from her worries.
「彼女は心配性の強い傾向があり、気が休まる日がない」
never gets a day off from one's worries で「気が休まる日はない」
別の例文：
ーShe has a propensity towards worrying which is a shame because she has everything she needs to be happy in her life.
「彼女は幸せな生活を送る全てを持っているのに、心配性の傾向があって残念だ」
ご参考まで！
オーストラリア 
カナダ 
