من عادة صديقتي أن تتأخر قليلا.

It uses a very common Arabic pattern:

من عادة + noun/pronoun + أن + verb

This pattern means it is someone's habit to... or someone tends to...

So:

• من عادة صديقتي = it is my friend's habit
• أن تتأخر = to be late
• قليلا = a little / a bit

A natural English rendering is: My friend tends to be a little late.

Here من is part of an idiomatic expression. It does not mean a literal from in normal English translation.

In this structure, من عادة... means something like:

• it is in the habit/nature/custom of...
• it is typical of...

So you should learn من عادة X أن... as a set phrase meaning it is typical/habitual for X to...

Here عادة is a noun, meaning habit or custom.

• عادة = a habit / the habit
• عادةً with tanwīn fatḥ is usually an adverb meaning usually

So in this sentence:

• من عادة صديقتي = it is my friend's habit
• not usually my friend...

That is why the plain noun عادة is used here.

The base word is صديقة = female friend.

When you attach a suffix like ـي for my, the ة becomes pronounced and written as ت before the suffix:

• صديقة = female friend
• صديقتي = my female friend

This is very normal with taa marbūṭa (ة). When a suffix is added, it behaves like ت.

Because it refers to صديقتي, which is feminine singular.

The verb تتأخر means she is late / she becomes late / she arrives late, depending on context.

So the agreement is:

• صديقتي = my female friend
• تتأخر = she is late

Arabic verbs must agree with the subject in gender, so the feminine form is required here.

After expressions like من عادة..., Arabic commonly uses أن + imperfect verb to express to do something.

So:

• أن تتأخر = to be late / that she is late

In English, we might say:

• It is my friend's habit to be a little late
• My friend tends to be a little late

So أن introduces the action that is the habit.

Yes. After أن, the imperfect verb is normally in the subjunctive.

So fully vocalized, it would be:

• indicative: تتأخرُ
• after أن: تتأخرَ

But in normal Arabic writing, short vowels are usually not written, so both appear as تتأخر.

That means the grammatical change is real, even though you usually do not see it in everyday text.

The verb comes from تأخر, which can mean:

• to be late
• to come late
• to be delayed
• to lag behind

In this sentence, the natural meaning is to be a little late or to arrive a little late.

So it is not just about physical delay in an abstract sense; in context, it describes your friend habitually being late.

قليلا means a little / a bit / slightly.

Here it works adverbially, modifying the verb تتأخر:

• تتأخر قليلا = she is a little late / she is late by a little

This word is in the accusative form, which is very common for adverb-like words in Arabic.

So even though English uses an adverb like a little, Arabic often uses a noun/adverbial expression in the accusative: قليلا.

Arabic usually does not use a present-tense verb to be in simple sentences like this.

So in the present tense, Arabic often says the equivalent of:

• From my friend's habit that she is a little late

without a separate word for is.

The meaning is understood automatically. This is normal in Arabic nominal-style sentences.

If you wanted past tense, then a verb like كان might appear.

Yes. Several variations are possible and natural:

• من عادتها أن تتأخر قليلا = It is her habit to be a little late
• عادتها أن تتأخر قليلا = Her habit is to be a little late
• من عادة صديقتي التأخر قليلا = using the verbal noun التأخر

All are understandable. The original sentence is a good, standard MSA sentence.

You can say that, but it means something slightly different in emphasis.

• صديقتي تتأخر قليلا = My friend is a little late / My friend comes a little late
• من عادة صديقتي أن تتأخر قليلا = My friend tends to be a little late / It is her habit to be a little late

The longer version emphasizes habit or usual behavior, not just one instance.