The student needs a mini lesson on revising run-on sentences and using transition words between sentences.
Mini Lesson Example:
If there is a sentence on both sides of a FANBOY (for, and, nor, but, or, yet) it is a compound sentence and you need a comma. If you do not put a comma then it is called a RUN-ON SENTENCE.
Examples:
She walked, and he ran.
I jumped around, or I sat still.
I like pizza everyday, but Bob and Mike do not.
The student also needs to transition from when the dog is at home and when the dog is at the dog show. The student should rewrite the passage as follows:
Once upon a time there was a lady named Margaret, and she was running on her treadmill. Her dog wanted to run with her, and she said, "No!" The dog stepped on the treadmill with her, and they both fell down! A month later, the dog was in a dog show *and saw a treadmill at the show. Margaret was afraid the dog would want to run on it, and she was right. The dog walked on the treadmill, and the dog was kicked out of the show.
*you DO NOT need a comma here because "saw a treadmill at the show" is not a complete sentence. You only need a comma before your conjunction (for, and, nor, but, or, yet) if there is a sentence on BOTH sides of the conjunction (for, and, nor, but, or, yet).