Hon lovade att fundera på mitt förslag och starta om datorn innan hon skickade nästa fil.

Because Swedish, like English, often leaves out the second infinitive marker when two infinitives are coordinated.

• Hon lovade att fundera på mitt förslag och starta om datorn = She promised to think about my proposal and restart the computer.

The att belongs to both infinitives:

• att fundera
• (att) starta

You could repeat att in some contexts, but it is usually unnecessary here.

Fundera på is the normal expression for think about / consider something.

• fundera = think, reflect
• fundera på något = think about something, consider something

So:

• fundera på mitt förslag = think about my proposal

This is something learners usually just have to memorize as a verb + preposition combination.

Because förslag is a neuter noun in Swedish, an ett-word.

Swedish possessives change to match the gender/number of the noun:

• min = for en-words
• mitt = for ett-words
• mina = for plural nouns

Examples:

• min bok = my book
• mitt förslag = my proposal
• mina böcker = my books

So förslag is ett förslag, therefore mitt förslag.

Datorn is the definite singular form: the computer.

• en dator = a computer
• datorn = the computer

In Swedish, the definite article is usually added as a suffix:

• bok → boken
• bil → bilen
• dator → datorn

So starta om datorn means restart the computer, not just restart a computer.

Yes, it functions as a particle verb, similar to English start up, turn off, or log in.

• starta om = restart / reboot

The particle om adds the idea of again / מחדש—in this context, restart.

Examples:

• Jag måste starta om datorn. = I have to restart the computer.
• Kan du starta om systemet? = Can you restart the system?

So you should learn starta om as a unit.

Because innan by itself introduces the subordinate clause. Swedish does not use att after innan in this kind of sentence.

• innan hon skickade nästa fil = before she sent the next file

Compare:

• Jag åt innan jag gick. = I ate before I left.
• Hon ringde innan mötet började. = She called before the meeting started.

So innan already does the job that before does in English.

Because innan hon skickade nästa fil is a new clause, and clauses normally need their own subject.

Main clause:

• Hon lovade ...

Subordinate clause:

• innan hon skickade nästa fil

Even though it is the same person, Swedish still repeats the subject, just as English does:

• She promised ... before she sent the next file.

You cannot normally omit the second hon here.

Skickade is the preterite/simple past form of skicka.

• skicka = send
• skickade = sent
• har skickat = has sent / have sent
• skickat = past participle, used with har/hade

In a past narrative sentence like this, Swedish very often uses the simple past:

• Hon lovade ... innan hon skickade nästa fil.

That is perfectly natural.
If you used hade skickat, it would change the timeline and sound more like before she had sent the next file, which is a different nuance.

After words like nästa, Swedish usually does not add the definite ending to the noun.

So you say:

• nästa fil = the next file
• nästa vecka = next week
• nästa gång = next time

Even though English often uses the in translation, Swedish usually just uses nästa + noun.

So nästa fil is the normal form.

It connects the two infinitive phrases:

• att fundera på mitt förslag
• (att) starta om datorn

So the structure is:

• Hon lovade
  att fundera på mitt förslag
  och starta om datorn
  innan hon skickade nästa fil

In other words, she promised to do two things:

1. think about the proposal
2. restart the computer

No, not in standard Swedish here.

Use:

• innan + clause
  • innan hon skickade nästa fil

or

• innan + noun phrase
  • innan mötet
  • innan nästa fil

But not innan att in this sentence.

Lovade is the preterite/simple past of lova.

• lova = promise
• lovar = promises / is promising
• lovade = promised
• lovat = promised (past participle)

So:

• Hon lovade ... = She promised ...

This sets the whole sentence in the past.

Yes. It is very normal.

The basic structure is:

• Hon = subject
• lovade = finite verb
• att fundera på mitt förslag och starta om datorn = infinitive phrase
• innan hon skickade nästa fil = subordinate time clause

So the sentence follows a very standard pattern:

1. subject
2. finite verb
3. the rest of the sentence

Inside the subordinate clause, the order is also normal:

• hon skickade nästa fil

Most naturally, it applies to the whole promised action: she promised to think about the proposal and restart the computer before sending the next file.

Because of the structure, many readers will understand the before-clause as giving the time frame for what she promised to do.

However, in real life, context helps. If needed, Swedish could be rewritten to make the scope clearer. But as written, the sentence is perfectly natural.

Yes. Fundera på often has that broader sense.

Depending on context, it can mean:

• think about
• reflect on
• consider

So Hon lovade att fundera på mitt förslag can sound like:

• She promised to think about my proposal.
• She promised to consider my proposal.

That is a good example of how one Swedish phrase can match several natural English translations.