Þó að hún sé ákveðin, hlustar hún samt á ráð þegar hún treystir fólki.

Because sé is the present subjunctive of vera (to be).

After þó að (although / even though), Icelandic very often uses the subjunctive, especially in a concessive clause like this one. So:

• hún er = she is, indicative
• hún sé = she be / is, subjunctive

In modern English, this distinction usually is not visible, but in Icelandic it is an important grammar point.

Þó að introduces a concessive subordinate clause. It sets up a contrast, like:

• although
• even though

So the clause Þó að hún sé ákveðin gives background that contrasts with what comes next.

You may also see þótt, which can often be used similarly.

This is because Icelandic follows a verb-second pattern in main clauses.

When the sentence begins with a whole subordinate clause, that clause takes the first slot:

• Þó að hún sé ákveðin = first slot

Then the finite verb of the main clause comes next:

• hlustar

Then the subject:

• hún

So:

• Þó að hún sé ákveðin, hlustar hún samt ...

If there were no fronted subordinate clause, you would normally get:

• Hún hlustar samt ...

Samt means still / nevertheless / all the same.

Yes, þó að already creates contrast, but samt reinforces it. Icelandic often uses both together very naturally:

• Þó að ... , ... samt ...

That gives the sentence a stronger sense of:

• even so
• despite that
• still

So samt is not redundant; it is a very common and idiomatic extra marker of contrast.

Because hlusta is normally used with the preposition á when you say what someone is listening to.

So Icelandic says:

• hlusta á tónlist = listen to music
• hlusta á ráð = listen to advice

This is just part of the verb pattern and needs to be learned as a unit:

• hlusta á + accusative

It can be tricky, because ráð has the same form in several cases and numbers.

The noun ráð is neuter, and:

• nominative/accusative singular: ráð
• nominative/accusative plural: ráð

So the form itself does not tell you immediately whether it is singular or plural.

In this sentence, it is best understood as advice in a general sense, not necessarily as a countable plural like pieces of advice. Icelandic often uses ráð this way.

Because Icelandic often uses bare nouns when speaking in a general sense.

Here the sentence is talking about:

• advice in general
• people in general

So indefinite, article-less forms are perfectly natural:

• á ráð
• treystir fólki

If the sentence meant specific advice or specific people, a definite form might be used instead.

Here ákveðin means something like determined or decisive.

The adjective agrees with hún, which is:

• feminine
• singular
• nominative

So the adjective appears in the feminine singular nominative form:

• masculine: ákveðinn
• feminine: ákveðin
• neuter: ákveðið

Because it is describing hún, ákveðin is the correct form.

Because the verb treysta takes the dative case when it means trust.

So:

• fólk = nominative/accusative
• fólki = dative

And the pattern is:

• treysta einhverjum = trust someone

That is why the sentence says:

• hún treystir fólki

This is a very useful verb to memorize together with its case.

Because þegar here introduces a normal time clause: when or whenever.

The sentence is describing a regular or real situation:

• she listens to advice when/whenever she trusts people

So the ordinary present indicative treystir is the natural choice.

The subjunctive is not normally needed here; the special subjunctive trigger in this sentence is þó að, not þegar.

Fólk is a collective noun. Grammatically, it is singular, but in meaning it refers to people as a group.

So:

• it means people
• but its grammar is singular/neuter

That is why you get forms like:

• fólk
• fólki

This is very common in Icelandic and worth getting used to early.

Because Icelandic normally keeps an explicit subject in each clause.

This sentence has several clauses:

• Þó að hún sé ákveðin
• hlustar hún samt á ráð
• þegar hún treystir fólki

Each clause needs its own subject, so repeating hún is completely normal. Icelandic does not usually drop subject pronouns the way some other languages do.

Because the opening part is a subordinate clause, and Icelandic commonly separates it from the main clause with a comma:

• Þó að hún sé ákveðin, hlustar hún samt ...

So the comma helps show the boundary between:

• the concessive subordinate clause
• the main clause

This kind of punctuation is very normal in Icelandic.