tough cookie

自分の意思がしっかりした人、(心が強い人)
主に女性に使うっぽい

Ex

  • She’s a tough cookie!

Reference source

  • https://ejje.weblio.jp/content/tough+cookie
  • https://www.collinsdictionary.com/dictionary/english/tough-cookie
  • http://getreadyforpmp.blogspot.com/2013/08/shes-tough-cookie.html
  • http://askshigeko.com/article/よく聞く表現3:tough-cookie