Even though Janie is with her dog, she is still the singular subject, so the verb must be "walks," not "walk." If the sentence read "Janie and her poodle Fido walk to the park," that would be correct, but the subject of the sentence only becomes plural if the word "and" connects Janie and Fido.
Test Prep Lessons With Video Lessons and Explained MCQ
Large number of solved practice MCQ with explanations. Video Lessons and 10 Fully explained Grand/Full Tests.