Meine Freundin ruft den Makler morgen noch einmal an, weil die Wohnungssuche allein zu lange dauert.

Because Makler is the direct object of the verb anrufen.

• der Makler = nominative, used for the subject
• den Makler = accusative, used for the direct object

In this sentence, meine Freundin is the subject, and she is calling the realtor/agent, so Makler must be in the accusative:

• Meine Freundin ruft den Makler an.

Because anrufen is a separable verb.

The full verb is anrufen = to call / phone someone.
In a normal main clause, the verb splits:

• Meine Freundin ruft den Makler an.

So:

• ruft = the conjugated part
• an = the separable prefix, which goes to the end of the main clause

This is very common in German:

• Ich stehe früh auf.
• Er kauft im Supermarkt ein.

But in some other structures, the verb does not split, for example in the infinitive:

• Sie will den Makler anrufen.

German word order is different in main clauses and subordinate clauses.

Main clause

German usually puts the finite verb in second position:

• Meine Freundin ruft den Makler morgen noch einmal an

Here, ruft is the finite verb, so it appears in position 2.

Subordinate clause

After a subordinating conjunction like weil, the finite verb usually goes to the end:

• weil die Wohnungssuche allein zu lange dauert

So dauert goes to the end because the clause starts with weil.

Weil means because and introduces a subordinate clause.

That is why the clause after it has different word order:

• weil die Wohnungssuche allein zu lange dauert

Compare:

• Denn = because, but usually keeps normal main-clause word order
• Weil = because, and sends the finite verb to the end

For example:

• Sie ruft an, weil sie eine Frage hat.
• Sie ruft an, denn sie hat eine Frage.

Both can mean the same thing, but the structure is different.

Noch einmal means again or one more time.

So:

• morgen noch einmal = again tomorrow / one more time tomorrow

It suggests that she has probably already called before and will call again.

You may also hear:

• noch mal
• nochmals

These are common alternatives in everyday German.

German adverb order is flexible, but some orders sound more natural than others.

Here:

• morgen = time
• noch einmal = repetition / manner-like information

So morgen noch einmal sounds natural: first the time, then the idea of repeating the action.

You could sometimes hear slight variations, but this version is very normal and idiomatic.

Here allein means alone or by oneself.

It refers to doing the apartment search alone:

• die Wohnungssuche allein = the apartment search alone / searching for an apartment by oneself

So the idea is that searching alone is taking too long.

In this sentence, allein works adverbially, describing how the search is being done.

Because zu lange means too long, not just long.

• lange dauern = to take a long time
• zu lange dauern = to take too long

So the sentence means that the apartment search is not just long, but longer than acceptable or convenient.

Examples:

• Das dauert lange. = That takes a long time.
• Das dauert zu lange. = That takes too long.

Because German very often makes compound nouns.

Wohnungssuche is made from:

• Wohnung = apartment
• Suche = search

Together:

• Wohnungssuche = apartment search / the search for an apartment

This is extremely common in German. The last part usually determines the grammatical gender, so because die Suche is feminine, the whole compound is feminine:

• die Wohnungssuche

In German compounds, the last noun usually decides the gender.

Here the final part is Suche, and it is feminine:

• die Suche

So the whole compound is also feminine:

• die Wohnungssuche

That is why the sentence has:

• weil die Wohnungssuche ... dauert

Because Freundin is feminine singular and here it is the subject of the sentence, so it is in the nominative case.

For feminine nominative singular, the possessive determiner takes -e:

• meine Freundin

Compare:

• mein Freund = my boyfriend / male friend
• meine Freundin = my girlfriend / female friend

So meine matches the feminine noun Freundin.

Yes, usually anrufen means to call someone on the phone.

So:

• jemanden anrufen = to call someone

That is why den Makler anrufen is a very natural phrase for contacting the realtor/agent by phone.

If German wants to be more specific, it can also use expressions like:

• telefonieren
• jemanden telefonisch kontaktieren

But anrufen is the normal everyday verb here.

Makler can mean broker or agent, depending on context.
In this sentence, because of die Wohnungssuche, it is naturally understood as a real-estate agent / realtor.

So the context tells you which kind of Makler is meant. Without context, the word can be broader, but here the housing context makes the meaning clear.