Hún gleður ömmu sína með litlu símtali á hverjum sunnudegi.

Gleður is the 3rd person singular present tense of að gleðja.

Because the subject is hún = she, Icelandic uses the matching finite verb form:

• að gleðja = to make happy, to gladden
• hún gleður = she makes happy / she gladdens

So gleðja is the dictionary form, but gleður is the form that fits this sentence.

Because amma is the direct object of gleður, it has to be in the accusative case.

The noun declines like this in the singular:

• amma = nominative
• ömmu = accusative

So:

• Hún gleður ömmu sína = She makes her grandmother happy

Even though ömmu can also be the same form in other cases, its job here is accusative object.

Because sína is the reflexive possessive, used when the possessor is the subject of the sentence.

Here, the subject is hún, and the grandmother belongs to her, so Icelandic uses sinn/sín/sitt rather than hennar.

• ömmu sína = her own grandmother / her grandmother where her refers back to the subject
• ömmu hennar would usually mean her grandmother, where her refers to some other female, not the subject

So this is a very important distinction in Icelandic.

It agrees with the thing possessed, not with the possessor.

So sína matches ömmu, which is:

• feminine
• singular
• accusative

That is why the form is sína.

A useful way to think about it:

• the subject decides whether you need a reflexive possessive
• the possessed noun decides the form of that possessive

That is very normal in Icelandic. Possessive words like minn, þinn, sinn often come after the noun.

So Icelandic commonly says things like:

• amma mín = my grandmother
• ömmu sína = her own grandmother

This is different from English, where the possessive usually comes before the noun.

Because the preposition með here is followed by the dative, so both the adjective and the noun have to be in dative form.

Breakdown:

• símtal = phone call
• símtali = dative singular
• lítill = little, small
• litlu = dative singular neuter, agreeing with símtali

So:

• með litlu símtali = with a little phone call

It is closer to by means of here.

So the idea is:

• she makes her grandmother happy by giving / through / with a little phone call

It is not really about physical accompaniment. It expresses the means by which she cheers her grandmother up.

This is a common Icelandic way to express a repeated time: every Sunday.

In this phrase:

• á = on
• hverjum = every, each, in the dative singular masculine
• sunnudegi = Sunday, in the dative singular

So literally it is something like:

• on each Sunday

But natural English is simply:

• every Sunday

Because it has to agree with sunnudegi.

The noun sunnudagur is:

• masculine
• singular
• here in the dative after á in this time expression

So hver changes to hverjum to match it.

You can think of it like this:

• hvaða dagur? type of word changes form to match the noun
• á hverjum sunnudegi = on every Sunday

Because Icelandic main clauses normally follow the V2 rule: the finite verb tends to come in the second position.

Here the first element is the subject:

• Hún = first position

So the verb comes next:

• gleður = second position

Then come the object and other phrases:

• ömmu sína
• með litlu símtali
• á hverjum sunnudegi

You could also move another element to the front, but the verb would still stay second:

• Á hverjum sunnudegi gleður hún ömmu sína með litlu símtali.

That is very typical Icelandic word order.