اختي في القطر دلوقتي.

The word is made of:

• أخت / اخت = sister
• -ي = my

So أختي / اختي literally means my sister.
Arabic very often expresses possession by attaching a suffix directly to the noun instead of using a separate word like my.

In careful standard spelling, you would normally write أختي with the hamza on أ.

In everyday Egyptian writing, especially in texting or informal writing, people often leave that hamza off, so اختي is very common. It does not change the meaning.

In Arabic, present-tense sentences like this usually do not use a separate word for is / am / are.

So:

• اختي في القطر دلوقتي = My sister is on the train now

This is completely normal in Arabic.
If you wanted the past, you would use a form of كان. In Egyptian negative present sentences, you often use مش, for example:

• اختي مش في القطر دلوقتي = My sister isn’t on the train now

In connected speech, في + ال often comes out sounding like fil-.

So في القطر is said roughly like fil-'aṭar in Egyptian pronunciation.

A couple of useful pronunciation notes:

• في = fi
• ال = el / il
• Egyptian ق is often pronounced as a glottal stop in Cairo-style speech

So learners may hear something like fil-'aṭar rather than a very careful word-by-word pronunciation.

In Egyptian Arabic, القطر is a common everyday word for the train.

If you know Modern Standard Arabic, you may expect القطار instead. That is the more formal/standard version. So:

• القطر = everyday Egyptian
• القطار = formal / MSA

Both refer to a train, but the sentence you were given is clearly colloquial Egyptian.

Arabic often uses في (in) where English uses on for vehicles.

So:

• في القطر literally looks like in the train
• but the natural English translation is on the train

This is just a normal difference between the two languages.

It can look confusing at first, because قطر is also the name Qatar.

But in this sentence, القطر means the train. A few clues help:

• the meaning of the sentence
• the presence of ال
• Egyptian colloquial usage

If you meant the country, you would usually say في قطر = in Qatar, without ال.

دلوقتي means now, right now, or at the moment.

It is a very common Egyptian colloquial word, not a formal one.
In Modern Standard Arabic, you would usually say الآن instead.

You may also see spelling variants such as:

• دلوقتي
• دلوقت

They are the same basic word in colloquial use.

The given order is very natural:

• اختي في القطر دلوقتي

But Arabic word order is somewhat flexible, especially with time words like دلوقتي. You could also hear:

• اختي دلوقتي في القطر
• دلوقتي اختي في القطر

These versions are all understandable. The difference is mainly one of emphasis or flow, not core meaning.

A more formal / Modern Standard Arabic version would be:

• أختي في القطار الآن

This means the same thing, but it sounds standard and formal rather than everyday Egyptian speech.