Learn Hardcore German: Meine Freundin sagt, ihre neue WG sei sehr ordentlich. - My friend says her new shared flat is very tidy.

With direct speech:
Meine Freundin sagt: „Meine neue WG ist sehr ordentlich.“
With indirect speech:
Meine Freundin sagt, ihre neue WG sei sehr ordentlich.

Using sei signals “I’m just reporting what she says; I’m not necessarily confirming it myself.”
You can say … dass ihre neue WG sehr ordentlich ist, especially in everyday conversation, but sei is the more “textbook” indirect-speech form.

What exactly is the form sei? How is it formed from sein?

Sei is the 3rd person singular Konjunktiv I (subjunctive I) of sein in the present tense.

Konjunktiv I of sein (present):

ich sei
du seiest
er / sie / es sei
wir seien
ihr seiet
sie seien

In the sentence, the understood subject of the clause is sie (meaning she / her WG), so you get sie sei → ihre neue WG sei.

Could I also say Meine Freundin sagt, dass ihre neue WG sehr ordentlich ist? Is that equivalent?

Yes, that’s a very common alternative:

Meine Freundin sagt, dass ihre neue WG sehr ordentlich ist.

Differences:

mit „dass“ + Indikativ (ist):
Very common in spoken German and neutral in tone. Used all the time.
ohne „dass“ + Konjunktiv I (sei):
Typical in more formal or written German (newspapers, reports) to mark indirect speech more clearly.

Both sentences are grammatically correct and express the same content. In everyday conversation, … dass ihre neue WG sehr ordentlich ist is more frequent.

What does WG mean, and what gender is it?

WG is an abbreviation for Wohngemeinschaft.

Meaning: a shared apartment / shared flat, where several people live together but are not necessarily a family or a couple.
Full word: die Wohngemeinschaft
Gender: feminine
→ die WG, eine WG, ihre neue WG

That’s why in the sentence you see ihre neue WG with feminine endings (ihre, -e on neu).

Why is it ihre neue WG and not ihrer neuen WG? What case is it in?

In ihre neue WG sei sehr ordentlich, ihre neue WG is the subject of the clause. Subjects are typically in the nominative case.

Nominative feminine singular:

article: die
possessive: ihre
adjective: neue
noun: WG

So you get: ihre neue WG.

If it were in another case, the forms would change, e.g.:

Dative: in ihrer neuen WG (in her new flat)
Genitive: ihrer neuen WG (of her new flat)

Here, since it’s the subject (“her new WG is tidy”), nominative ihre neue WG is correct.

Does ihre here mean “her” or “their”? How do I know?

Ihre can mean several things, depending on context:

her (possessive pronoun referring to sie = she)
their (possessive pronoun referring to sie = they)
your (formal, referring to Sie = you-formal)

In this sentence:

The main subject is Meine Freundin (my girlfriend / female friend).
Then we get: … sagt, ihre neue WG sei sehr ordentlich.

The most natural reading is:

ihre refers back to meine Freundin, so it means her.

If the broader context had a plural sie (“they”) as the last relevant subject, ihre could mean their. But with just this one sentence, default interpretation is “her new WG”.

Why is the verb sei at the end of the clause ihre neue WG sei sehr ordentlich?

German subordinate clauses (Nebensätze) usually put the finite verb at the end.

Here the sentence has an embedded clause of reported speech after sagt. It’s structurally similar to a dass-clause, even though dass is omitted:

Full version: Meine Freundin sagt, dass ihre neue WG sehr ordentlich sei.
Without dass: Meine Freundin sagt, ihre neue WG sei sehr ordentlich.

Because it functions like a dass-clause, the verb (here: sei) goes to the final position of that clause, just as ist would in:

… dass ihre neue WG sehr ordentlich ist.

Why is there a comma before ihre neue WG sei sehr ordentlich?

The comma separates the main clause from the subordinate (reported-speech) clause.

Main clause: Meine Freundin sagt
Subordinate / reported clause: ihre neue WG sei sehr ordentlich

Even though there is no explicit conjunction like dass, German still treats this as a separate clause and requires a comma.

So you always write:

Sie meint, er komme später.
Er behauptet, das stimme nicht.

How is ordentlich different from other words like sauber or aufgeräumt?

All three can relate to neatness, but they focus on different aspects:

ordentlich
- “tidy”, “orderly”.
- Things are in their proper places; structure and order are good.
- Can also imply someone is organized or disciplined.
sauber
- “clean” (not dirty).
- Focuses on cleanliness, not whether things are well-arranged.
aufgeräumt
- literal: “tidied up”.
- Focuses on the result of tidying—things have just been put away neatly.

So sehr ordentlich suggests the WG is very tidy and well-organized, not just free of dirt.

Does Freundin always mean “girlfriend” in the romantic sense?

Not always. Freundin can mean:

girlfriend (romantic partner)
female friend

Which one it is depends on context.

If someone says meine Freundin about an adult and there’s no extra context, listeners often assume a romantic relationship.
To make clear it’s just a friend, people might say:
- eine Freundin von mir (a friend of mine, female)
- meine gute Freundin (my good [female] friend), depending on tone and situation.

In your sentence alone, Meine Freundin is ambiguous, but in everyday use it usually suggests “my girlfriend” unless clarified otherwise.

Is it common in spoken German to use sei, or do people usually just say ist?

In everyday spoken German, most people prefer:

… dass ihre neue WG sehr ordentlich ist, or even
Sie sagt, ihre neue WG ist sehr ordentlich.

Using Konjunktiv I (sei) is:

very common in formal writing (news reports, official statements)
used by speakers who want to sound a bit more formal or precise

So:

In conversation with friends: … ist is more natural.
In written reports / news: … sei is very typical.