Jędrzejczak was born in Ruda Śląska, Silesian Voivodship, Poland. She started swimming at the age of six as a measure to correct a slight curvature of the spine. At first she hated the sport. Her attitude towards it changed after she had won her first prize in a competition in Germany at the age of eight. Jędrzejczak took up swimming seriously in high school. Led by coach Maria Jakóbik, she won her first titles in the Junior European Championships in 1999. Medals in the Senior European Championships in 1999 and 2000 opened the way to her first Olympic appearance.