Saumavélin hennar er gömul, en hún virkar enn vel þegar hún saumar gardínur.

Because Icelandic usually adds the definite article to the end of the noun instead of using a separate word like the.

• saumavél = sewing machine
• saumavélin = the sewing machine

So saumavélin hennar literally looks like the sewing machine of hers, but the natural English meaning is her sewing machine.

That is a very common Icelandic pattern with possessives.

In English, we say her sewing machine.
In Icelandic, it is very natural to say:

• saumavélin hennar = her sewing machine
• bíllinn hans = his car
• bókin mín = my book

So the structure is often:

noun + definite article + possessive

This is one of the first word-order differences English speakers usually notice.

Because adjectives in Icelandic must agree with the noun in gender, number, and case.

Here, saumavélin is:

• feminine
• singular
• nominative

So the adjective gamall takes the feminine singular nominative form gömul.

Basic forms are:

• masculine: gamall
• feminine: gömul
• neuter: gamalt

So:

• Saumavélin er gömul = The sewing machine is old

This is a very common source of confusion.

In this sentence:

• the first hún refers to saumavélin = the sewing machine
• the second hún refers to the woman = she

Why can hún mean both she and it here? Because Icelandic pronouns follow grammatical gender.

Since saumavél is a feminine noun, it can be referred to as hún, even though it is an object in English and would be it.

So Icelandic can do this:

• Saumavélin ... hún virkar = The sewing machine ... it works

Then later:

• þegar hún saumar = when she sews

Context tells you which hún is meant.

Because Icelandic often refers back to nouns using pronouns that match the noun’s grammatical gender.

So an inanimate noun can be:

• hann if the noun is masculine
• hún if the noun is feminine
• það if the noun is neuter

Since saumavél is feminine, the sewing machine is referred to as hún.

This is different from English, where inanimate things are usually just it.

Here enn means still.

So:

• virkar enn vel = still works well

In other contexts, enn can sometimes be understood as yet, but here still is the natural meaning.

Because vel is an adverb, and it modifies the verb virkar.

• góður / góð / gott = good as an adjective
• vel = well as an adverb

Compare:

• Hún er góð = She is good
• Hún virkar vel = It works well

Since the sentence is describing how it works, Icelandic uses the adverb vel.

Both are present tense, third person singular verb forms.

• virka = to work / function
• sauma = to sew

In this sentence:

• hún virkar = it works
• hún saumar = she sews

So the -r ending is a very common present-tense ending for he/she/it.

Because the sentence is talking about a habitual or general situation, not one single event happening right now.

So the idea is:

• It still works well when she sews curtains
• meaning whenever she sews curtains or in that kind of situation

Icelandic, like English, often uses the present tense for habits and general truths.

Þegar means when.

So:

• þegar hún saumar gardínur = when she sews curtains

It introduces a time clause, just like when in English.

Gardínur is the direct object of saumar, so it is in the accusative plural.

She is sewing curtains, so the noun must be plural.
For many feminine nouns, the plural forms can look similar, so learners may not immediately notice the case function just from the ending.

What matters here is:

• saumar gardínur = sews curtains

So gardínur is the thing being sewn.

Yes: the sentence is very natural Icelandic word order.

Break it up like this:

• Saumavélin hennar er gömul
• en hún virkar enn vel
• þegar hún saumar gardínur

That gives:

1. subject: Saumavélin hennar
2. verb: er
3. description: gömul
4. contrast with en = but
5. another clause: hún virkar enn vel
6. time clause: þegar hún saumar gardínur

So even though some details differ from English, the overall sentence structure is not unusually difficult once you understand the possessive pattern and the pronouns.