http://www.spanishdict.com/topics/show/107 Looks like the answer is that "consider" is an intransitive verb and only transitive verbs use the personal "a" (for the direct object.) He isn't receiving any action. (Sorry! Techinically...) She's considering. The thoughts her brain manufactures are the (unspoken) direct object and he is merely the indirect object.
Although the link you provided is very useful, it only proves that the verb "consider" IS transitive. Consider what? Consider this. Think it over. Take this into consideration. In the given example, however, the syntax is slightly different. We are dealing with secondary predication here. In simple terms, when we say, "Consider X (to be) Y", we mean "Think that X is Y". As we learn from the Spanish sentence presented by DL, in this structure no personal 'a' should be used. That is the only explanation.