Hún finnur strokleðrið sitt í töskunni eftir að hún gerir lítil mistök.

Sinn/sín/sitt is the reflexive possessive pronoun. It is used when the possessor is the same as the subject of the clause.

So:

• Hún finnur strokleðrið sitt = She finds her own eraser
• Hún finnur strokleðrið hennar would usually mean She finds her eraser, where her refers to some other female, not to the subject herself

This is a very common thing English speakers need to get used to in Icelandic.

Because sinn/sín/sitt agrees with the thing being possessed, not with the person who possesses it.

Here, the possessed noun is strokleðrið, which is:

• neuter
• singular
• accusative

So the correct form is sitt.

Even though the owner is she, the pronoun does not become feminine just because the owner is feminine.

It may look strange from an English point of view, but this is a normal Icelandic pattern.

In Icelandic, when a possessive pronoun comes after the noun, the noun is often definite:

• bókin mín = my book
• húsið mitt = my house
• strokleðrið sitt = her own eraser

So although it looks like the eraser her-own word-for-word, it is simply the normal way to say it.

Because í takes different cases depending on meaning:

• í + dative for location: in
• í + accusative for motion into something: into

Here the meaning is location, not movement:

• í töskunni = in the bag
• í töskuna = into the bag

So töskunni is the dative singular definite form of taska.

Eftir að is a conjunction meaning after when it introduces a full clause:

• eftir að hún gerir lítil mistök = after she makes small mistakes

By contrast, eftir by itself is usually a preposition and is followed by a noun phrase:

• eftir mat = after dinner
• eftir skólann = after school

So here eftir að is needed because what follows is a full clause with a subject and verb.

Because eftir að hún gerir lítil mistök is a full subordinate clause, and a full clause normally needs its own subject.

English also repeats the subject in a sentence like after she makes mistakes, and Icelandic does the same.

If you want to avoid repeating hún, Icelandic can use an infinitive construction instead:

• eftir að hafa gert lítil mistök = after making small mistakes / after having made small mistakes

Because the sentence can be understood as a general or habitual statement: this is what happens whenever she makes small mistakes.

So the present tense works well:

• Hún finnur ... eftir að hún gerir ...

If you wanted to talk about one specific past event, you would normally use the past tense:

• Hún fann strokleðrið sitt í töskunni eftir að hún gerði lítil mistök.

Yes. The normal expression is að gera mistök, which means to make mistakes.

This is just the standard verb-noun combination in Icelandic. Learners often need to memorize these combinations, because they do not always match English word-for-word.

So:

• gera mistök = make mistakes

Because the adjective must agree with mistök in gender, number, and case.

Mistök here is:

• neuter
• plural
• accusative

The correct form of lítill for neuter plural nominative/accusative is lítil.

So:

• lítið = neuter singular
• lítil = neuter plural
• litla is a different form used in other grammatical environments

That is why lítil mistök is correct.

It is plural: mistakes.

That is why the adjective is also plural:

• lítil mistök = small mistakes

Also, mistök is very commonly used as a plural noun in Icelandic. In this sentence it is indefinite, so there is no definite article: small mistakes, not the small mistakes.

Here are the main ones:

• finnur → að finna = to find
• gerir → að gera = to do / to make
• töskunni → taska = bag
• strokleðrið → strokleður = eraser
• mistök is usually learned as mistök = mistakes

This matters because Icelandic words often change form a lot depending on case, number, gender, and tense.

In this sentence, yes, it looks fairly similar:

• Hún finnur strokleðrið sitt í töskunni eftir að hún gerir lítil mistök.

But Icelandic has a verb-second pattern in main clauses, so word order becomes more noticeably different when something else is moved to the front.

For example:

• Eftir að hún gerir lítil mistök finnur hún strokleðrið sitt í töskunni.

Here the main verb finnur still comes early in the main clause. So this sentence is a good example of Icelandic looking simple on the surface, while still following its own word-order rules.