Ona je prijateljica.

Because prijateljica is the feminine form meaning female friend. Since ona means she, the noun referring to her is also feminine.

• prijatelj = male friend / friend (masculine)
• prijateljica = female friend (feminine)

Serbian usually matches gender like this:

• On je prijatelj. = He is a friend.
• Ona je prijateljica. = She is a friend.

Je is the 3rd person singular form of the verb biti (to be), so here it means is.

A few forms of biti in the present tense are:

• ja sam = I am
• ti si = you are
• on/ona/ono je = he/she/it is
• mi smo = we are
• vi ste = you are
• oni/one/ona su = they are

So:

• Ona je prijateljica. = She is a friend.

Yes, very often.

Serbian often drops subject pronouns when they are already clear from context, because the verb form usually tells you the person.

So both of these are possible:

• Ona je prijateljica.
• Je prijateljica.

However, in normal standard Serbian, if the pronoun is omitted, people more naturally say:

• Prijateljica je.

Why? Because je is a short unstressed form, and these short forms usually do not stand at the beginning of a sentence.

So:

• Ona je prijateljica. = perfectly normal
• Prijateljica je. = also normal
• Je prijateljica. = usually avoided as a standalone sentence

Because Serbian has no indefinite article like English a/an.

So:

• prijateljica can mean a friend
• in some contexts it can also mean friend

Serbian also does not normally use a word equivalent to English the in the same way. Whether something is definite or indefinite is usually understood from context.

So Ona je prijateljica naturally means She is a friend.

Not as fixed as in English.

Ona je prijateljica. is a normal neutral order, but Serbian allows some flexibility depending on emphasis.

For example:

• Ona je prijateljica. = neutral
• Prijateljica je. = emphasizes what she is
• Ona prijateljica? = not correct as a normal statement
• Je ona prijateljica? = possible in a question-like structure, but not the neutral statement form

One important rule here is that je is a clitic: a short unstressed word that usually takes the second position in the sentence or clause. That is why Ona je prijateljica sounds natural.

A rough guide is:

pri-ya-TELY-ee-tsa

A few helpful points:

• pri sounds roughly like pree
• ja sounds like ya
• lj is a special Serbian sound, similar to the lli in million for many English speakers
• ca at the end sounds like tsa

So prijateljica is approximately: pree-ya-TELY-ee-tsa

The exact Serbian pronunciation is more precise than English spelling can show, but that rough version is a good start.

Lj is a single Serbian letter/sound, not just an ordinary l plus j.

It is pronounced like a soft l. Many English speakers find it similar to:

• the lli in million
• or the li in some pronunciations of brilliant

Examples:

• prijatelj = friend
• ljubav = love
• bolji = better

It is a very common sound in Serbian, so it is worth practicing early.

Usually prijateljica means female friend.

If you want to say girlfriend in the romantic sense, Serbian often uses:

• devojka = girlfriend / girl
• sometimes context can also clarify meaning

So in a basic sentence like:

• Ona je prijateljica.

the natural meaning is She is a friend, not She is a girlfriend.

It is in the nominative case.

In this sentence:

• Ona is the subject
• je is the verb
• prijateljica is a predicate noun after to be

With biti (to be) in the present tense, Serbian normally uses the nominative for this kind of sentence:

• On je doktor.
• Ona je studentkinja.
• Ona je prijateljica.

So prijateljica is in its basic dictionary form here.

Yes, in many situations.

Drugarica also means female friend, but it has a slightly different feel depending on region, age, and context.

Very roughly:

• prijateljica = friend, often a bit more neutral or standard
• drugarica = friend, buddy, school friend, companion; sometimes feels more informal or youthful

Both are real and common words, but prijateljica is a very safe, standard choice for learners.

The pronoun can be included for several reasons:

• to make the subject clear
• to add emphasis
• to contrast with someone else
• because the speaker simply chooses to say it

For example:

• Ona je prijateljica, a on je komšija.
  = She is a friend, and he is a neighbor.

Here the pronouns help make the contrast clear.

So even though Serbian often omits pronouns, using ona is completely natural.

You would use nije (is not):

• Ona nije prijateljica. = She is not a friend.

Here:

• je = is
• nije = is not

This pattern is very common:

• On je student. → On nije student.
• Ona je prijateljica. → Ona nije prijateljica.

One common way is:

• Da li je ona prijateljica? = Is she a friend?

Another possible form is:

• Je li ona prijateljica?

In speech, intonation also matters, but for learners, Da li je... ? is a very useful and clear pattern.

So:

• statement: Ona je prijateljica.
• question: Da li je ona prijateljica?