categories have been implemented as they are now a number of years back. They're structured in a sort of russian doll structure. Some are more comprehensive (i.e. Vampires) than others (Denali coven), and it has been decided that they shouldn't appear alongside each other on pages. Irina is a member of the Denali coven, which is vampire-only; no need to reiterate she's also a vampire.
I've reverted your edits and hope I won't have to do it again. Thanks!