Why does it seem that everything that I read in philosophy always uses "she" or "her" instead of "his" or "he"?
This is the effect of a successful political movement, one that sought to replace the use of "he" and "his", as "gender-neutral" pronouns, with the use of something else. The reason was that people thought that the use of "he" and "his", at least in certain contexts, made readers liable to assume that the pronoun referred to a person of the male persuasion, when it need not. One option is to use something that is truly gender-neutral, such as "he or she", but that is rather verbose. Some people therefore use "s/he", but that is ugly. I've taken to using "s'he", but I'm lonely. And there is a case to be made for "she" and "her", unaltered, as well, namely that it makes one conscious of something of which one might not otherwise have been conscious.