After being seriously injured by the Nephilim, Hibiki is unable to control her Symphogear.  She flies into a rage, destroying the Nephilim and ripping out its heart.  During the post-fight medical exam, it's discovered that if she continues to use her gear, she'll die.
That's why she's still happy, even after they died.
لهذا ظلّتْ سعيدة حتّى بعد وفاتهما
Deshalb freut sie sich auch
nach deren Tod noch so sehr.
Por eso puede estar tan feliz 
aunque todos murieran.
Por eso puede estar tan 
contenta aunque todos murieran.
Elle va bien,
contrairement aux morts.
Ovvio che è tutta contenta,
anche se sono morti.
Por isso que ela continua bem, 
mesmo que morram.