Translation:On the way home, she ate seventeen apples.
SNĚDLA (inf. SNÍST) is a perfect verb (aspect) while JÍST is imprefect. Ona jedla = she was eating. Ona snědla = she ate. The apples are gone. Some of these perfect verbs do not really exist in present tense. They only have past and future.
You can easily have a sentence MY TO JÍME (present) AŽ TO SNÍME (future tense). which would be "we are eating it till we finish it (eat it)"