Here's why:
* Missing a verb: The sentence lacks a verb that shows action or a state of being. We need a verb to connect the subject "you" to the object "she."
* Incomplete thought: The phrase doesn't convey a complete thought. It leaves the reader wondering what "you" stopped "she" from doing.
To fix the fragment, you could add a verb:
* "You stopped her from running."
* "You stopped her at the door."
* "You stopped her in her tracks."
These examples provide the necessary verb to complete the sentence and make it grammatically correct.