It was the other way around, Philip was trying to conquer Greece and he figured sending a threatening letter to Sparta might be enough, since at that point they were about powerless.
So the invasion was always planned and the courtesy of the answer didn’t matter.
I think you should tell her as a parent that she shouldn’t spend time with boys and instead focus on her studies. No way that will backfire!
But seriously though what does “failing” even mean here, how can a 13 years old “fail”?