Ella es una vegetariana vs ella es vegetariana
I learned to use "ella es vegetariana", if I wanted to say she is a vegetarian. Granted, "vegetariana" can also be used as an adjective, which would, if intended to be used, make the sentence correct I think. But if I dont want to use the word as an adjective, but as a noun, are either sentences correct? "Ella es una vegetariana" and "ella es vegetariana". I was wondering, because it seems to me that the "una" is missing in the 2nd sentences, which is normally used in sentences like these, for example " ella es una mujer".
What is it?
Sorry if I'm just repeating information you already know, but the indefinite article (un or una) is omitted with jobs and occupations, which vegetariana falls under, but mujer does not. You'd also say Ella es mecánica ("She's a mechanic") or Él es doctor ("He's a doctor"). If you're not there already, I believe it's covered in the "People" unit.
This - dropping the "a(n)" before a job - is the case for almost every European language - Spanish, Italian, French, German, Swedish, and Russian, among others.
You're right in thinking that it's also an adjective, but it doesn't make much sense with the article - imagine saying "She is a happy" or "It is a red". Same logic applies to Spanish, at least in this area.
I hope I answered your question.
The thing is that there are words that have a default function, for example, words like "vegetariano" and "humano" are adjectives (their default function), but they can also work as nouns, so saying "Ella es vegetariana" or "Ella es humana" is completely normal, but using nouns in any of those sentences would make it sound weird, the noun form would be better used in a different sentence, like for example: "Ella es Ana, una vegetariana que ocasionalmente come carne".
The word "mujer", which you also mentioned above, is a noun by default, hence "Ella es una mujer" is a common phrasing, nevertheless, it can also work as an adjective, not to identify gender, but to talk about someone's attributes, so it would not be weird to hear "Ella es mujer" or "Yo soy hombre", neither of these two is accepted by Duolingo though, I've tried.