Learn Hardcore German: Meine Cousine ist Studentin an der Universität und studiert Biologie. - My cousin is a university student and studies biology.

Cousine is a feminine noun (die Cousine).
In this sentence, Cousine is the subject, so it’s in the nominative case.
The nominative feminine form of mein is meine.

So:

Meine Cousine = my (female) cousin (subject, nominative feminine)
You would say Mein Cousin for a male cousin (because Cousin is masculine).

Why is it Cousine and not Cousin here?

German distinguishes between male and female cousins with different words:

der Cousin = male cousin
die Cousine = female cousin

The sentence talks about Meine Cousine, so it’s clearly referring to a female cousin, hence the form Cousine.

Why is there no article in ist Studentin? Why not ist eine Studentin?

In German, when you state someone’s profession, role, or status using sein (to be), you normally omit the article:

Sie ist Studentin. = She is a (university) student.
Er ist Lehrer. = He is a teacher.
Ich bin Arzt. = I am a doctor.

You can use eine Studentin if you want to emphasize something like “one (of many) students” or contrast her with others, but in neutral statements about someone’s occupation or role, no article is standard.

So Meine Cousine ist Studentin is the most natural way to say “My cousin is a (female) student.”

Why Studentin and not Student?

Studentin is the feminine form of Student:

der Student = male student
die Studentin = female student

Since we are talking about Cousine (a female person), the noun referring to her profession also takes the feminine form: Studentin.

This pattern with -in for the feminine is very common in professions and roles:

Lehrer → Lehrerin
Arzt → Ärztin
Freund → Freundin

Why do we say an der Universität instead of in der Universität?

Both an and in can mean “at” in English, but they’re used differently:

an der Universität studieren / arbeiten
= to be enrolled or employed at a university (institutional sense)
in der Universität
= inside the building of the university (physical location)

In this sentence, the focus is that she studies at a university as an institution, not that she’s physically located inside its buildings at this moment. That’s why an der Universität is used.

Compare:

Sie studiert an der Universität.
She is a university student there (institutional).
Sie sitzt in der Universität und lernt.
She is sitting inside the university building and studying (physical location).

Why is it an der Universität and not an die Universität?

An is a two-way preposition (Wechselpräposition) that can take:

Accusative when there is movement towards something
Dative when it is about a location without movement

Here we talk about where she is enrolled / studies, not about moving to the university. So we use the dative:

die Universität (nominative)
der Universität (dative singular, feminine)

So:

an der Universität = at the university (dative, static location)
an die Universität gehen = to go to the university (accusative, movement)

Why is Universität capitalized? And why is Biologie capitalized?

In German, all nouns are capitalized, regardless of whether they are common nouns or proper names.

Universität is a common noun (university) → capitalized.
Biologie is the name of a school subject / field of study → also a noun → capitalized.

So whenever you see a German word referring to a person, thing, place, idea, or subject (a noun), it will normally start with a capital letter.

Why is there no article before Biologie in studiert Biologie?

Names of school subjects and academic fields usually appear without an article in German when you talk about what someone studies or learns:

Sie studiert Biologie.
Er studiert Medizin.
Wir lernen Deutsch.

Using die Biologie would sound unusual here; it would suggest a more specific meaning (“the biology of something”), not the subject as a general field. For the general field of study, no article is standard.

What’s the difference between ist Studentin and studiert Biologie? Aren’t they saying almost the same thing?

They are related but not identical:

ist Studentin an der Universität tells you
- her status/role (she is a student)
- and where (at the university).
studiert Biologie tells you
- her academic activity / field (she studies biology, that’s her subject or major).

Combined, the sentence says:
She’s a university student and her field of study is biology.

You could say just one part:

Meine Cousine studiert Biologie. (implies she is a university student in biology)
Meine Cousine ist Studentin. (just says she is a student; doesn’t say what subject)

Could I say Meine Cousine studiert an der Universität Biologie? Is that word order correct?

Yes, that word order is grammatically correct:

Meine Cousine studiert Biologie an der Universität.
Meine Cousine studiert an der Universität Biologie.

Both are possible. Typically:

Shorter and less “heavy” information comes earlier.
Many speakers prefer studiert Biologie an der Universität, because Biologie is closely connected to the verb studiert.

But German word order inside the “middle field” of a main clause is relatively flexible, as long as the finite verb stays in second position:

Meine Cousine (position 1 – subject)
studiert (position 2 – finite verb)
Biologie an der Universität (rest of the sentence, order flexible)

Why is it just studiert and not something like “is studying” in German?

German doesn’t have a separate progressive tense like English “is studying”.
The simple present in German covers both:

Sie studiert Biologie.
= She studies biology.
= She is studying biology. (ongoing situation)

Context tells you whether it’s a general fact or something happening right now. For long-term activities like a course of study, the simple present already implies an ongoing process.

What is the difference between studieren and lernen? Could I say Meine Cousine lernt Biologie?

Both mean “to study / learn”, but they’re used differently:

studieren
- mainly about university-level study or a subject as a major
- Sie studiert Biologie. = She is enrolled in biology (as her degree subject).
lernen
- more general; to learn or study in the sense of doing homework, memorizing, preparing
- Sie lernt Biologie. = She is learning/working on biology (e.g. for a test), not necessarily as her degree.

So for describing her degree program, studieren is the natural verb:
Meine Cousine studiert Biologie.

Could I add sie and say: Meine Cousine ist Studentin an der Universität und sie studiert Biologie?

Yes, that is grammatically correct, but a bit more explicit than necessary.

In German, when two clauses share the same subject and are joined with und, you can omit the repeated subject in the second part:

Meine Cousine ist Studentin an der Universität und studiert Biologie.
(subject Meine Cousine applies to both verbs)

Adding sie:

Meine Cousine ist Studentin an der Universität und sie studiert Biologie.

This is fine if you want to emphasize the subject again or make the sentence very clear for learners, but native speakers often leave the second sie out in such cases.