Take another look at the sentence:
With a hotdog, Dris __________ Butler, her bulldog, to the car but could not get him onto the backseat; Butler sensed a trip to the vet and refused to budge.
The sentence requires the simple past of lead, an irregular verb. Led is the simple past form.
|Verb||Simple Present||Simple Past||Past Participle|
Leaded, the form you chose, is a spelling error. Before you continue, review the rules for irregular verbs.