Is it permissible to communicate with a young man who is not a mahram via phone or email to discuss educational matters concerning a younger brother, knowing that there is no desire for this and that the matter may not be repeated?

The fundamental principle governing relationships between the sexes (frequent correspondence and conversation) is prohibition. There is absolutely no necessity for a girl to converse with a non-mahram (definition) young man under the pretext of supervising her younger brother educationally. Satan attempts to mislead those committed to religion by making forbidden relationships appear legitimate, such as mutual advice or exchanging books. Educational supervision of the younger brother can be undertaken by an older brother, the father, a mahram relative, or the mother, in order to thwart Satan and block avenues of temptation.