اول ما رجعت اختي من الشغل، شافت علبة العصير.

In Levantine, أول ما is a very common expression meaning when or as soon as.

So:

• أول ما رجعت اختي من الشغل = When / As soon as my sister came back from work

Literally, أول means first, but in this pattern أول ما works like a fixed expression, not a word-for-word first what translation.

It often introduces the first action in a sequence:

• أول ما وصلت، اتصلت فيني = As soon as she arrived, she called me

Because Arabic spelling without short vowels can leave some past-tense forms looking identical. The key is the context.

Here, رجعت اختي tells you that اختي is the subject, so رجعت must mean she came back.

In other words:

• رجعت by itself can be ambiguous in writing
• but once you add اختي right after it, the meaning becomes clear: my sister came back

This is very normal in Arabic.

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

So this is natural:

• رجعت اختي = my sister came back

You could also say:

• اختي رجعت

That is also correct, but it feels a bit different in emphasis. Very roughly:

• رجعت اختي = more narrative, event-focused
• اختي رجعت = more topic-focused, with extra attention on my sister

Both are normal in Levantine.

اختي means my sister.

It is made of:

• أخت / اخت = sister
• ـي = my

So:

• اختي = my sister

In everyday Levantine pronunciation, this is often said something like ekhte or ikhti, depending on the speaker and region.

من الشغل is the normal colloquial way to say from work.

Here:

• من = from
• الشغل = the work / work

Even though English usually says just from work without the, Arabic often uses the definite article in these everyday expressions.

So من الشغل sounds very natural in Levantine.

You will hear similar patterns in speech:

• راح عالمدرسة = he went to school
• رجع من الجامعة = he came back from الجامعة / from the university

شافت is the past tense feminine singular form of شاف, which means to see in Levantine.

So:

• شاف = he saw
• شافت = she saw

Since the subject is اختي = my sister, the verb has to match a feminine singular subject.

That is why the sentence uses شافت, not شاف.

Because Arabic verbs already carry subject information.

So شافت already includes the idea of she saw, and رجعت here is understood as she came back because of the subject اختي.

Arabic often does not need an extra pronoun like هي unless you want emphasis or contrast.

For example:

• شافت علبة العصير = she saw the juice carton
• هي شافت علبة العصير = she saw the juice carton with extra emphasis on she

Because this is an idafa construction, often called a possessed or linked noun phrase.

Here:

• علبة = carton / box / container
• العصير = the juice

Together:

• علبة العصير = the juice carton / the carton of juice

In an idafa:

• the first noun usually does not take ال
• the second noun can take ال
• the whole phrase gets its definiteness from the second noun

So علبة العصير is correct, while العلبة العصير is not.

It is definite here.

That may seem surprising because علبة itself does not have ال, but in an idafa construction the whole phrase becomes definite if the second noun is definite.

Since العصير has ال, the whole phrase is definite:

• علبة العصير = the juice carton

Compare:

• علبة عصير = a juice carton / a carton of juice
• علبة العصير = the juice carton

It can often mean either one, depending on context.

In many everyday Levantine sentences, أول ما strongly suggests as soon as or right when:

• أول ما وصلت، نمت = As soon as I arrived, I slept

But in some contexts, English when is the most natural translation.

So in your sentence, both ideas are close:

• When my sister came back from work, she saw the juice carton
• As soon as my sister came back from work, she saw the juice carton

One possible pronunciation is:

awwal ma rjiʕit ekhte mn ish-shoghol, shaafet ʕelbit il-ʕaseer

A few notes:

• اول is usually awwal
• رجعت may sound like rjiʕit or something close, depending on region
• اختي often sounds like ekhte
• الشغل is often ish-shoghol or esh-sheghl, depending on dialect
• شافت is usually shaafet
• علبة may sound like ʕelbe / ʕelbit in connected speech

Exact pronunciation varies a lot across Levantine dialects, so small differences are completely normal.