Learn Hardcore German: Meine Kommilitonin hilft mir bei der Hausarbeit. - My fellow female student helps me with the term paper.

Kommilitonin means a female fellow student at a university or similar higher-education institution, usually someone studying the same subject or on the same course.

Comparisons:

Freundin = (female) friend / girlfriend. It says nothing about studying with you.
Kollegin = (female) colleague at work, not at university.
Mitschülerin / Klassenkameradin = (female) classmate at school (not university).

So you use Kommilitonin specifically in a university/college context for a fellow student who is female.

Why is it Meine Kommilitonin and not Mein Kommilitonin?

Because Kommilitonin is grammatically feminine and here it is the subject (nominative case).

The base possessive is mein.
In the nominative feminine, mein gets an -e ending: meine.

Patterns in the nominative:

mein Vater (masculine)
meine Mutter (feminine)
mein Kind (neuter)
meine Freunde (plural)

So with a feminine noun in subject position, you must say meine Kommilitonin.

What is the masculine form and the plural forms of Kommilitonin?

The base word is:

der Kommilitone = male fellow student
die Kommilitonin = female fellow student

Plurals:

die Kommilitonen = plural for males or a mixed group
die Kommilitoninnen = plural for women only

Examples:

Meine Kommilitonen sind sehr nett. – My fellow students (mixed or all male) are very nice.
Meine Kommilitoninnen und Kommilitonen helfen mir. – My female and male fellow students help me.

Why is the verb hilft and not helft or hilftet?

The infinitive is helfen (to help), which is an irregular verb with a vowel change (e → i) in the singular.

Present tense of helfen:

ich helfe
du hilfst
er / sie / es hilft
wir helfen
ihr helft
sie / Sie helfen

The subject Meine Kommilitonin = sie (3rd person singular), so you must use hilft:

Meine Kommilitonin hilft ... – She helps ...

Why is it hilft mir and not hilft mich?

Because helfen always takes the dative case, not the accusative.

mich = accusative form of ich
mir = dative form of ich

So you have:

Sie hilft mir. – She helps me.
Sie sieht mich. – She sees me.

Some other verbs that also take the dative are danken (to thank), gefallen (to please), and gehören (to belong).

What case is der Hausarbeit, and why do we use der and not die?

Hausarbeit is a feminine noun: die Hausarbeit.

After the preposition bei, you must use the dative case. For feminine nouns, the dative singular article changes from die to der:

Nominative: die Hausarbeit
Accusative: die Hausarbeit
Dative: der Hausarbeit

So:

bei der Hausarbeit = with / during the homework/housework/term paper

The article der here is dative feminine, not masculine.

Why do we say bei der Hausarbeit and not mit der Hausarbeit or für die Hausarbeit?

The choice of preposition changes the meaning:

bei der Hausarbeit = while doing / with / in the context of the Hausarbeit:
She supports you in that activity. This is the standard way to say “helps me with my _.”
mit der Hausarbeit would sound like “together with the Hausarbeit” (the homework is her companion), which is odd. It does not normally mean “with the homework” in the sense of helping.
für die Hausarbeit = for the Hausarbeit (for the sake of it, for the purpose of it), e.g.
Sie sammelt Informationen für die Hausarbeit. – She collects information for the term paper.

So when you want to say “help someone with something,” in German you normally use:
jemandem bei etwas helfen.

What exactly does Hausarbeit mean here—household chores or school/university work?

It can mean different things depending on context:

Household chores / housework
- In everyday family/home contexts, die Hausarbeit usually means housework (cleaning, cooking, etc.).
- Then the sentence means: My fellow student helps me with the housework.
Academic work (term paper / written assignment)
- In a university context, die Hausarbeit very often means a term paper / written assignment for a course.
- Then it means: My fellow student helps me with the term paper.

If you want to be clear:

die Hausaufgaben = homework (usually school)
im Haushalt helfen / bei den Hausarbeiten helfen = help with household chores
eine Hausarbeit schreiben = write a term paper

Can we change the word order? For example, can we say Bei der Hausarbeit hilft mir meine Kommilitonin or Meine Kommilitonin hilft bei der Hausarbeit mir?

German word order is flexible, but not all orders sound natural.

These are fine and common:

Meine Kommilitonin hilft mir bei der Hausarbeit.
– Neutral, standard order.
Bei der Hausarbeit hilft mir meine Kommilitonin.
– Emphasis on bei der Hausarbeit (e.g. in contrast to something else she doesn’t help with).
Mir hilft bei der Hausarbeit meine Kommilitonin.
– Emphasis on mir or on meine Kommilitonin (maybe in contrast to someone else).

This sounds unnatural in normal speech:

*Meine Kommilitonin hilft bei der Hausarbeit mir.

Pronouns like mir, dir, ihm usually come before longer phrases like bei der Hausarbeit, not after. So keep mir before the prepositional phrase.

Is Hausarbeit countable? Can I say eine Hausarbeit or viele Hausarbeiten?

Yes, but it depends on the meaning:

Academic term paper / written assignment
- eine Hausarbeit schreiben – to write a term paper
- zwei Hausarbeiten abgeben – to hand in two term papers
  Here, Hausarbeit is countable and the plural Hausarbeiten is normal.
Housework / chores (general activity)
- Often treated more like an uncountable activity:
  Die Hausarbeit ist anstrengend. – Housework is tiring.
- You can say die Hausarbeiten for “the chores,” but many speakers prefer other specific words like Aufgaben im Haushalt, Putzarbeiten, etc.

In your sentence, both readings are possible; context decides.

How does the pronoun mir change for other persons, and what would the sentence look like with different pronouns?

Mir is the 1st person singular dative form of ich. Here are the dative pronouns:

ich → mir
du → dir
er → ihm
sie (she) → ihr
es → ihm
wir → uns
ihr → euch
sie (they) → ihnen
Sie (formal you) → Ihnen

Examples with the same pattern jemand hilft jemandem bei etwas:

Meine Kommilitonin hilft dir bei der Hausarbeit. – My fellow student helps you with the Hausarbeit.
Mein Kommilitone hilft ihr bei der Hausarbeit. – My (male) fellow student helps her.
Unsere Kommilitoninnen helfen uns bei der Hausarbeit. – Our fellow students (female) help us.

The verb form also changes with the subject, but the object pronoun stays dative.

How do you say this sentence in the past and future tenses?

Most commonly you use the Perfekt (spoken past) and Futur I (future):

Perfekt (present perfect):
Meine Kommilitonin hat mir bei der Hausarbeit geholfen.
– My fellow student has helped me / helped me with the Hausarbeit.
Präteritum (simple past, more written style for this verb):
Meine Kommilitonin half mir bei der Hausarbeit.
Futur I (future):
Meine Kommilitonin wird mir bei der Hausarbeit helfen.
– My fellow student will help me with the Hausarbeit.

How do you pronounce Kommilitonin, and where is the stress?

Kommilitonin is pronounced approximately:

IPA: [kɔ.mi.liˈtoː.nɪn]
Syllables: Kom–mi–li–TO–nin

Details:

Stress is on the “to”: KommiliTOnin.
The o in the first syllable (Kom-) is short, helped by the double mm.
The o in -ton- is long: toː.

Is Kommilitonin commonly used in spoken German today, or are there more natural alternatives?

Kommilitonin is correct and understood everywhere, especially in academic contexts. It does sound a bit formal/academic in casual conversation.

In everyday speech, people might instead say, for example:

meine Mitstudentin – my fellow student
eine aus meinem Kurs / Seminar – a girl/woman from my course/seminar
meine Studienkollegin – my study colleague (regional, especially in Austria/Switzerland)

Your sentence with Kommilitonin is perfectly fine, especially in anything related to university life or in written German.