A B does not indicate a struggle. (Only on CC does B=Bad.) One B will not hurt her anywhere; no applicant was ever rejected based on a B. It is a myth that all boarding schools, even the most sought-after, are populated by all-A students. Just not true. So, let those concerns go, and help her focus on putting together an application that demonstrates how/where she is shiny to the schools that would be a good fit for her.
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