قالت الاستاذة في الاجتماع إن القرار مهم.

Because Arabic often uses verb + subject order, especially in straightforward narration.

So قالت الأستاذة... is a very normal way to say the teacher said...

You can also say الأستاذة قالت..., but that usually gives a bit more emphasis to the teacher.

Because الأستاذة is feminine, so the past-tense verb must be feminine too.

• قال = he said
• قالت = she said

Since الأستاذة means a female teacher/professor, قالت is the correct form.

In careful MSA, the standard spelling is الأستاذة with a hamza: أ.

So the fully standard form is:

• الأستاذة

Many people omit hamza in casual typing and write الاستاذة, but in formal Arabic you should write الأستاذة.

This is taa marbuuTa (ة), a very common marker of feminine nouns.

Here it shows that the noun is feminine:

• أستاذ = male teacher/professor
• أستاذة = female teacher/professor

At the end of a paused word, it usually sounds like -a / -ah. In grammatical pronunciation with endings, it behaves like a t sound.

في is the preposition in or at, and الاجتماع means the meeting.

So في الاجتماع means in the meeting or, more naturally in English, at the meeting.

This phrase tells you the setting of the speech: where or during what event the teacher said it.

Here إنّ introduces a reported statement, similar to English that.

So the structure is:

• قالت ... إن ...
• she said ... that ...

In normal unvoweled writing, you often see it written simply as إن, but grammatically it is إنّ.

Because إنّ is the usual particle for introducing a full reported clause like that the decision is important.

A learner should mainly remember this pattern:

• قال إنّ... = he said that...
• قالت إنّ... = she said that...

أن is used in other structures, so it is not the natural choice here.

It is not written, because Arabic usually omits the verb to be in the present tense.

So:

• القرار مهم
• literally: the decision important
• natural English: the decision is important

This is a very common Arabic pattern.

Because القرار مهم is a full sentence, not just a noun phrase.

• القرار = the decision
• مهم = important

Together they mean the decision is important.

If you said القرار المهم, that would mean the important decision, which is just a noun phrase, not a complete sentence.

So this difference is important:

• القرار مهم = the decision is important
• القرار المهم = the important decision

In normal Arabic writing, the short vowel endings are usually not shown, but the full grammatical form would be:

قالتِ الأستاذةُ في الاجتماعِ إنَّ القرارَ مهمٌّ.

Here is what is happening:

• الأستاذةُ: subject of قالت, so it is nominative
• الاجتماعِ: after the preposition في, so it is genitive
• القرارَ: the noun of إنّ, so it is accusative
• مهمٌّ: the predicate of إنّ, so it is nominative

You do not usually need to write these endings in everyday reading, but it is useful to know they are there.

Yes. Arabic allows some flexibility in word order.

For example, you could also say:

• في الاجتماع قالت الأستاذة إن القرار مهم

That is still grammatical, but it gives more emphasis to at the meeting.

The original order is neutral and very natural:

• قالت الأستاذة في الاجتماع إن القرار مهم