Many Ukrainian-Americans (people born in the west into Ukrainian families) end up using "є" for "to be" (am/is/are) even though native speakers apparently do not. I guess in written form a dash is sometimes used instead.
And thats the exact thing i miss on Ukrainian and Russian. As Slovak its just so weird not seeing it there
Well, if by a 'girlfriend' you mean a female friend, 'подруга' certainly could be translated as 'gf'.
If you'd like to refer to a girl or woman somebody's having a romantic relationship with, you should use '[кохана] дівчина'.
In English we'd say "My friend IS a student" but Ukrainian doesn't use the verb 'to be' in these cases. E.g. "I am a student" is simply "я студент" [literally: I student]. So I think the dash here is supposed to emphasise that the friend IS a student, a sort of = sign.
I know that Russian has some weird punctuation rules that aren't used in English but are not essential to translate the meaning. Perhaps this is also the case in Ukrainian and this is one example.
You don't need the dash when you are comparing to nouns/pronouns. e.g. 'I am a man'. You need a dash when there are more nouns/ pronouns My mother is a woman