My younger sister tends to squeeze in too many things into her schedule and end up not being able to complete some of them. Because of that, she starts panicking afterwards.
ご質問ありがとうございます。
"My younger sister tends to squeeze in too many things into her schedule"＝「私の妹はスケジュールにあまりにも詰め込み過ぎて」
"and end up not being able to complete some of them."＝「結局、全ては終わらせることができなくなってしまう。」
"Because of that, she starts panicking afterwards."＝「それによって、後からパニックに彼女はなる。」
ご参考に！
アメリカ合衆国 
