Min søster sætter to alarmer, fordi hun ellers kommer til at slumre igen.

Because søster is a common-gender noun in Danish, and common-gender nouns take min in the singular.

• en søster = a sister
• min søster = my sister

If the noun were neuter, you would use mit instead:

• et hus = a house
• mit hus = my house

So the choice of min / mit depends on the gender of the noun, not on the speaker.

In Danish, a possessive like min, din, hans, vores usually replaces the definite article.

So:

• søster = sister
• min søster = my sister

You do not normally say min søsteren for my sister.

This works much like English, where you say my sister, not my the sister.

Literally, sætter often means sets, puts, or places depending on context. In this sentence, it means sets in the sense of setting an alarm.

So:

• at sætte en alarm = to set an alarm

A natural English translation would be sets two alarms.

In everyday Danish, many speakers also say stiller en alarm. Depending on context and region, both can be heard, but sætter here is completely understandable and natural.

Because to means two, and alarmer is the plural form of alarm.

• en alarm = an alarm
• to alarmer = two alarms

Danish nouns often form the plural with -er, and alarm does that here.

So the pattern is:

• singular indefinite: en alarm
• plural indefinite: alarmer

Fordi means because. It introduces the reason.

So the sentence structure is:

• Min søster sætter to alarmer = main statement
• fordi hun ellers kommer til at slumre igen = reason

Together:

• My sister sets two alarms because otherwise she ends up snoozing again

It is one of the most common Danish conjunctions for giving a reason.

Because fordi introduces a subordinate clause, and subordinate clauses in Danish usually have different word order from main clauses.

In a main clause, Danish often follows verb-second order:

• Hun kommer ellers til at slumre igen is not the most natural main-clause version, but you can compare:
• Ellers kommer hun til at slumre igen = Otherwise, she will end up snoozing again

In a subordinate clause after fordi, the finite verb usually comes after sentence adverbs like ellers:

• fordi hun ellers kommer til at slumre igen

So the pattern is:

• fordi + subject + adverb + verb

That is why ellers comes before kommer here.

Here ellers means otherwise.

So:

• fordi hun ellers kommer til at slumre igen = because otherwise she’ll end up snoozing again

It signals what would happen if she did not set two alarms.

Ellers can have a few meanings in Danish depending on context, but otherwise is the one that fits here.

Kommer til at + infinitive is a very common Danish structure. It often means:

• end up doing
• come to do
• do unintentionally / by accident
• sometimes simply happen to do

In this sentence:

• kommer til at slumre igen

means something like:

• ends up snoozing again
• will end up pressing snooze again

It suggests that this is not really her intention, but something that tends to happen.

So the full idea is: she sets two alarms because otherwise she will likely end up snoozing again.

Because slumre is in the infinitive, and after komme til Danish normally uses at + infinitive.

So the structure is:

• komme til at gøre noget = to end up doing something

Examples:

• Hun kommer til at glemme det = She will end up forgetting it
• Jeg kom til at sige det = I ended up saying it / I said it by accident

Here:

• kommer til at slumre = ends up snoozing

In this context, slumre means to snooze.

Because it is used with an alarm, it refers to using the snooze function instead of fully waking up.

So:

• slumre igen = snooze again

Outside this exact context, slumre can also mean doze or slumber, but with alarms it strongly suggests hitting snooze.

Igen means again, and its position here is very natural in Danish.

• slumre igen = snooze again

Putting igen at the end clearly modifies the action slumre.

This is similar to English, where again often comes after the verb phrase:

• do it again
• snooze again

So igen at the end sounds normal and idiomatic.

Yes. A more word-for-word version would be:

• Min søster = my sister
• sætter = sets
• to alarmer = two alarms
• fordi = because
• hun = she
• ellers = otherwise
• kommer til at = ends up / comes to
• slumre = snooze
• igen = again

So a fairly literal gloss is:

My sister sets two alarms because she otherwise ends up snoozing again.

That sounds a little unnatural in English, so a more natural translation would be:

My sister sets two alarms because otherwise she ends up snoozing again.