"She is bad at math."
Translation:Matematika jí jde špatně.
Non-linguistic remark: Great that Matej loves mathemaics, but a pity that she is bad at it. Maybe add a sentence that Katerina or Zofie or one of their daughters loves mathematics?
(I am a mathematician so I don't want to put anybody off math and hope that by good teaching, everyone will come to love it.)