Is Judy leads a charmed life she never seems to have a serious accident a run on sentence?

Yes, "Judy leads a charmed life; she never seems to have a serious accident" is a run-on sentence. It improperly combines two independent clauses without proper punctuation or a coordinating conjunction. To correct it, you could use a semicolon, a conjunction, or break it into two separate sentences. For example: "Judy leads a charmed life; she never seems to have a serious accident."