In der Kurzgeschichte geht es um ein Mädchen, das sein Umfeld mutig verändert.

Es geht um … is a very common German idiom meaning “it is about … / it concerns … / it deals with …”.

Literally, gehen means “to go”, so word‑for‑word it’s something like “it goes around (the topic of) …”, but you should treat es geht um as a fixed expression.

You generally don’t say ist über for “is about” in this context. Instead you use:

• Es geht um ein Mädchen. – “It is about a girl.”
• Der Film handelt von einem Mädchen. – “The film is about a girl.”

So in your sentence:

• In der Kurzgeschichte geht es um ein Mädchen …
  = “In the short story, it is about a girl … / the short story is about a girl …”

Here es is a dummy subject (also called an expletive pronoun). It doesn’t refer to any concrete thing; it just fills the subject position because German usually wants an explicit grammatical subject.

You can think of it like the “it” in English sentences such as:

• “It is raining.”
• “It seems that …”

Similarly:

• Es geht um ein Mädchen.
  Literally: “It goes about a girl.” → Idiomatic: “It’s about a girl.”

The real content of the sentence is in um ein Mädchen; es just keeps the grammar happy.

No, In der Kurzgeschichte es geht um ein Mädchen is incorrect word order.

German main clauses follow the V2 rule: the conjugated verb must be in second position (counting big phrases as one “slot”).

• Fronted phrase: In der Kurzgeschichte (1st position)
• Conjugated verb: geht (2nd position)
• Subject (dummy): es
• Rest: um ein Mädchen …

So the correct patterns are:

• In der Kurzgeschichte geht es um ein Mädchen.
• Es geht in der Kurzgeschichte um ein Mädchen.

In both cases, geht is in second position. Putting es right after the prepositional phrase would push the verb to third position, which violates V2 in main clauses.

The preposition in can take either dative or accusative, depending on meaning:

• Accusative (wohin? – where to?): movement into something
  
  • Ich gehe in die Kurzgeschichte ein. (very unusual phrasing; “I go into the short story” conceptually)
• Dative (wo? – where?): static location
  
  • In der Kurzgeschichte geht es um … = “In the short story, it is about …”

Your sentence describes where something takes place (inside the story), not movement into it, so dative is used:

• Feminine die Kurzgeschichte in dative singular → der Kurzgeschichte
  → in der Kurzgeschichte.

No. The gender of Kurzgeschichte is feminine:

• die Kurzgeschichte – “the short story” (nominative)

You see der here because the noun is in the dative case, not because it’s masculine.

Feminine singular definite article:

• Nominative: die Kurzgeschichte – Die Kurzgeschichte ist spannend.
• Dative: der Kurzgeschichte – In der Kurzgeschichte passiert viel.

So:

• In der Kurzgeschichte … = in + dative feminine.

Mädchen is grammatically neuter, even though it refers to a female person.

Reason: it ends in -chen, a diminutive ending; almost all -chen words are neuter:

• das Mädchen – the girl
• das Brötchen – the bread roll
• das Häuschen – the little house

So the correct article is:

• das Mädchen (nominative)
• ein Mädchen (indefinite article, nominative/accusative)

Eine Mädchen is incorrect because eine is the feminine form.

The relative pronoun must agree in gender and number with the antecedent (the noun it refers to). The antecedent is ein Mädchen, which is neuter singular:

• das Mädchen → das (neuter singular relative pronoun)

So:

• … ein Mädchen, das sein Umfeld mutig verändert.

If the noun were feminine, you’d use die:

• eine Frau, die ihr Umfeld mutig verändert.

If it were masculine:

• ein Junge, der sein Umfeld mutig verändert.

The comma marks the start of a relative clause:

• …, das sein Umfeld mutig verändert.

Relative clauses in German:

• Always start with a relative pronoun (der, die, das, den, dem, deren, etc.).
• Are normally set off by commas.
• Send the conjugated verb to the end.

So:

• ein Mädchen, das sein Umfeld mutig verändert
  → das introduces the clause, verändert goes to the end, and commas separate the clause from the main clause.

Grammatically, sein agrees with the grammatical gender of Mädchen, not the natural gender of the person.

• das Mädchen → neuter
• Neuter possessive: sein (“its / his” in grammar terms)

So:

• ein Mädchen, das sein Umfeld verändert
  = “a girl who changes its environment” (but in English we say her environment).

Standard written German usually sticks to this rule for Mädchen and other neuter person words (das Kind → sein Spielzeug).

In everyday spoken German, some people do say ihr Umfeld to reflect natural gender, but in formal/standard grammar sein Umfeld is considered correct for Mädchen.

Umfeld is a neuter noun: das Umfeld.

It usually means a person’s environment in a more figurative / social sense:

• social circle
• surroundings in terms of relationships, influences, conditions

Umgebung is more the physical surroundings:

• die Umgebung – the area, the neighborhood, the physical environment

In your sentence:

• sein Umfeld mutig verändert
  suggests she is bravely changing her social / personal environment (people around her, the structures, the situation she lives in), not just the physical space.

Mutig is originally an adjective (“courageous”), but German adjectives often act as adverbs without changing form. In this sentence it modifies the manner of the action:

• verändert = changes
• mutig verändert = changes bravely / courageously

Placement: German adverbs of manner usually come before the verb in simple structures:

• Sie verändert ihr Umfeld mutig.
• Sie läuft schnell. – She runs quickly.

You could also say:

• … das mutig sein Umfeld verändert.

Both das sein Umfeld mutig verändert and das mutig sein Umfeld verändert are possible, but putting mutig right before the verb is very natural.

All three verbs exist, but they differ slightly:

• ändern = to change (something)
  
  • Sie ändert ihre Meinung. – She changes her mind.
• verändern = to change, often with a nuance of more thorough or lasting change
  
  • Sie verändert ihr Umfeld. – She transforms / significantly changes her environment.
• sich verändern = to change oneself / to undergo change
  
  • Sie verändert sich. – She changes (her character, behavior, etc.).

In your sentence:

• sein Umfeld verändern = she actively changes the environment around her
  (not just a tiny tweak, usually implies a noticeable or substantial change)

So verändert is chosen to emphasize a stronger or more transformative change.

Both verbs are in the Präsens (present tense):

• geht es um – present
• verändert – present

German Präsens is quite flexible. It can express:

• present:
  
  • Right now, in this story, it is about a girl who is changing her environment.
• general truths / content:
  
  • This story (whenever you read it) is about a girl who changes her environment.
• scheduled / narrative present:
  
  • Used when summarizing plots, headlines, etc.

So here it’s essentially a timeless present used for plot summary / description of content.

Yes, several idiomatic alternatives exist. For example:

• Die Kurzgeschichte handelt von einem Mädchen, das sein Umfeld mutig verändert.
  (uses handeln von instead of es geht um)

• In der Kurzgeschichte wird von einem Mädchen erzählt, das sein Umfeld mutig verändert.
  (more like “In the short story, a girl is described who …”)

• Die Kurzgeschichte erzählt von einem Mädchen, das sein Umfeld mutig verändert.

Your original sentence is already correct and idiomatic; these are just stylistic variations.