هي كانت عم تدرس عربي لما اتصلت فيها صديقتها.

Yes, كانت already shows 3rd person feminine singular, so هي is not strictly necessary.

In Levantine, though, speakers often include subject pronouns even when the verb already shows the person and gender. It can make the sentence feel more natural in conversation, or it can help keep the topic clear.

So both of these work:

• هي كانت عم تدرس عربي...
• كانت عم تدرس عربي...

The version with هي is a little more explicit: as for her, she was studying Arabic...

This is the Levantine way to make a past continuous / past progressive idea:

• كانت = was
• عم تدرس = studying / is studying

Together:

• كانت عم تدرس = she was studying

A useful comparison:

• تدرس = she studies / she is studying
• عم تدرس = she is studying, with clear ongoing action
• كانت عم تدرس = she was studying

So the sentence is describing an action that was already in progress when something else happened.

عم is a very common Levantine marker for an action that is in progress.

So:

• عم تدرس = she is studying
• عم يكتب = he is writing
• عم ناكل = we are eating

In this sentence, عم helps show that the studying was ongoing, not just a completed event.

Without عم, the sentence would sound less clearly progressive in everyday Levantine.

Yes, you could, but it sounds less typically colloquial.

In spoken Levantine:

• كانت عم تدرس is the most natural way to say she was studying
• كانت تدرس can sound more formal, more literary, or sometimes less clearly focused on the ongoing nature of the action

So if you want natural everyday Levantine, كانت عم تدرس is the safer pattern.

In everyday Levantine, language names are often said in a shorter, more colloquial way.

So:

• عربي = Arabic
• إنجليزي = English
• فرنسي = French

After verbs like study, this is very normal:

• تدرس عربي
• بتحكي إنجليزي
• عم يتعلم فرنسي

In more formal Arabic, you would usually expect العربية instead of عربي in this sentence:

• تدرس العربية

So عربي here is a good sign that the sentence is colloquial Levantine.

Here, لما means when.

It introduces the event that happened during the ongoing action:

• هي كانت عم تدرس عربي لما اتصلت فيها صديقتها
• She was studying Arabic when her friend called her

So the timeline is:

1. she was already studying
2. then the call happened

In spoken Levantine, لما is a very common everyday word for when in this kind of sentence.

Because the subject is صديقتها = her friend, and that friend is female.

The base noun is:

• صديقة = female friend

So the verb has to match that feminine subject:

• اتصل = he called
• اتصلت = she called

That feminine -ت ending in the past tense is very common in Arabic.

It is made of:

• صديقة = female friend
• -ها = her

When a noun ending in ة takes a suffix, that ة becomes ت in spelling:

• صديقة
• صديقتها = her female friend

This happens with many nouns:

• سيارة = car

• سيارتها = her car

• مدرسة = school
• مدرستها = her school

So صديقتها literally means her female friend.

Because verb + subject order is very common in Arabic.

So this is normal:

• اتصلت فيها صديقتها

Literally, the order is closer to:

• called her her-friend

But in natural English, of course, you say:

• her friend called her

You could also put the subject first:

• صديقتها اتصلت فيها

That is also possible, but the version with the verb first is extremely common in Arabic storytelling and ordinary speech.

Because with اتصل in Levantine, the person being called is commonly expressed with a preposition + pronoun, not as a direct object.

So:

• فيها = her in this structure

This is something you mostly just learn as part of how the verb is used. In other words, you do not treat call someone here the same way English does.

Also, phone-related verbs vary a lot by region and style. You may hear other patterns too, such as:

• دقّت لها = she rang/called her
• حكت معها = she spoke with her

But in this sentence, اتصلت فيها is the chosen Levantine phrasing.

The clearest Levantine features are:

• عم as a progressive marker
• عربي instead of the more formal العربية
• the overall spoken-style phrasing

A more MSA-style version would be:

• كانت تدرس العربية حين اتصلت بها صديقتها

So if you compare them:

• Levantine: هي كانت عم تدرس عربي لما اتصلت فيها صديقتها
• MSA: كانت تدرس العربية حين اتصلت بها صديقتها

Both mean the same thing, but the original sentence sounds much more like everyday spoken Levantine.