هي تستشير أمين المكتبة في قاعة القراءة.

هي is not strictly necessary.

Arabic verbs already show the subject information, so تستشير by itself can mean she consults / is consulting. The sentence could therefore be:

تستشير أمين المكتبة في قاعة القراءة.

Adding هي does one or more of these things:

• makes the subject extra clear
• adds slight emphasis to she
• removes ambiguity, since تستشير can also mean you (masculine singular) consult

So in this sentence, هي is helpful and natural, but not required.

In the Arabic imperfect tense, the prefix تـ can mark different persons, including:

• she
• you (masculine singular)
• you (feminine singular), though the full form differs in some contexts

Here, because the sentence begins with هي, we know تستشير means she consults / she is consulting.

So:

• هي تستشير = she consults
• أنتَ تستشير = you (masculine singular) consult

This is one reason the explicit pronoun can be useful.

It can mean either one.

The Arabic imperfect often covers both:

• simple present: she consults
• present progressive: she is consulting

Context tells you which is meant. Without extra context, both are possible.

That is very normal in Arabic. You should not expect a separate verb form exactly like English is consulting every time.

تستشير comes from the verb استشارَ / يستشيرُ, from the root ش و ر.

This root is connected with the idea of:

• consultation
• advice
• deliberation

The verb استشار is a common Form X verb, and Form X often has the sense of seeking something. So استشار has the sense of seeking advice or consulting someone.

Useful related forms:

• استشارَ = he consulted
• يستشيرُ = he consults / is consulting
• تستشيرُ = she consults / is consulting
• مشورة = advice, consultation
• شورى = consultation

Because it is an iḍāfa construction, often called a genitive/possessive construction.

Literally:

• أمين = keeper, custodian, trustee
• المكتبة = the library

So أمين المكتبة literally means the keeper/custodian of the library, which idiomatically means the librarian.

This kind of expression is very common in Arabic. A job title is often built as:

noun + noun

where the first noun describes a role and the second noun tells you what it is connected to.

Because that is how iḍāfa works.

In an iḍāfa:

• the first noun usually does not take الـ
• the second noun determines whether the whole phrase is definite or indefinite

So:

• أمين مكتبة = a librarian / a library custodian
• أمين المكتبة = the librarian / the library’s custodian

Even though أمين has no الـ, the whole phrase is definite because المكتبة is definite.

In Arabic, استشار normally takes a direct object.

So you say:

• استشارَ الطبيبَ = he consulted the doctor
• تستشير أمينَ المكتبةِ = she consults the librarian

There is no extra preposition needed here.

A related but different verb is تشاور مع, which means something more like consult with / discuss with each other:

• تشاورَ مع زميله = he consulted with his colleague

So in this sentence, استشار / يستشير is the right pattern, and the person consulted appears as a direct object.

This is a prepositional phrase of place.

• في = in
• قاعة = hall
• القراءة = the reading

Together, قاعة القراءة is another iḍāfa, meaning reading hall or reading room.

So:

• في قاعة القراءة = in the reading hall / in the reading room

Grammatically:

• في makes the following noun genitive
• قاعةِ is therefore in the genitive
• القراءةِ is also genitive because it is the second term of an iḍāfa

Yes. Arabic word order is flexible.

Your sentence begins with the subject pronoun:

هي تستشير أمين المكتبة في قاعة القراءة.

A very natural alternative is simply:

تستشير أمين المكتبة في قاعة القراءة.

Starting with هي gives a clearer she and can sound slightly more emphatic or topical, like as for her, she consults...

So both are possible, but they do not feel exactly identical in emphasis.

With full vowel endings, the sentence is:

هِيَ تَسْتَشِيرُ أَمِينَ المَكْتَبَةِ فِي قَاعَةِ القِرَاءَةِ.

Here is why:

• هِيَ: independent pronoun
• تَسْتَشِيرُ: imperfect verb in the indicative, so it ends in ـُ
• أَمِينَ: direct object, so it is accusative
• المَكْتَبَةِ: second noun of an iḍāfa, so it is genitive
• فِي: preposition
• قَاعَةِ: after a preposition, so genitive
• القِرَاءَةِ: second noun of an iḍāfa, also genitive

In normal everyday writing, these short vowels are usually omitted, but they are still understood.

A careful pronunciation is:

hiya tastashīru amīna al-maktabati fī qāʿati al-qirāʾati

A few notes:

• تستشير = tastashīru
• أمين = amīn
• قاعة has the consonant ʿayn: qāʿa
• القراءة includes a hamza at the end: qirāʾa

If you are reading unvocalized Arabic, it is useful to know the fully vocalized form so the grammar and pronunciation become clearer.