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Answer: No, it is not a run-on sentence</h3>
This is one full thought that doesn't run on for too long. The "overcome with joy" portion is the dependent clause that needs the other part "Mrs. Monroe told her husband the exciting news about her promotion" which is the independent clause. The independent clause could be its own sentence without the dependent clause, but not the other way around.
Using my common sense and a bit of knowledge in English, I can infer that she feels strongly about her garden and loves it very much. This leads me to believe that she is a loving and caring character. If something is described vividly this generally means that 1) this is a good writer 2) they feel strongly about what they are writing 3) both a good writer and a strong feeling
I think the answer is either C. or D. But I think it's more like C.