tien ga atte, kanozyo ha syuuden ni maniau ka douka sinpaisite ita.

Because ある is being used: 遅延がある means there is a delay.

With nouns like 遅延, 問題, 事故, and 予定, Japanese often uses がある to express that something exists or occurs.

• 遅延がある = there is a delay
• 問題がある = there is a problem

So 遅延があって is literally something like there being a delay...

あって is the て-form of ある, and here it links the first part of the sentence to the main clause.

So:

• 遅延があって、... = because there was a delay, ... / there being a delay, ...

The て-form often gives background, cause, or a sequence of events.

Even though あって itself is not marked for past tense, the whole sentence is understood as past because the main verb is 心配していた.

A more explicit past/causal version could be:

• 遅延があったので、...
• 遅延があったから、...

But あって sounds natural and smooth here.

かどうか means whether or not.

It turns a clause into an embedded yes/no question:

• 終電に間に合うかどうか = whether she would make the last train or not

This is very common before verbs like:

• 知る = know
• 分かる = understand
• 確認する = confirm
• 心配する = worry

You can think of the structure as:

• [plain clause] + かどうか

Example:

• 行くかどうか分からない = I don’t know whether I’ll go or not.

Yes, you can.
終電に間に合うか心配していた is also natural.

The version with かどうか sounds a little fuller and more explicitly like whether or not. The version with just か is slightly more compact.

So:

• 終電に間に合うかどうか心配していた = worried about whether she would make the last train or not
• 終電に間に合うか心配していた = worried about whether she would make the last train

Both are fine.

Because 間に合う normally takes に, not を, for the thing you make it in time for.

So:

• 電車に間に合う = make the train
• 会議に間に合う = make it to the meeting in time
• 締め切りに間に合う = meet the deadline / make the deadline

The に marks the target time/event/deadline.

So 終電に間に合う means to be in time for the last train.

は marks 彼女 as the topic: as for her...

So the sentence is structured like:

• As for her, because of the delay, she was worried about whether she would make the last train.

Using は makes her the person the sentence is talking about.

If you used 彼女が, the nuance would be different. が would focus more on she as the specific person involved, often in a context where that identification matters.

Here, 彼女は is the most natural neutral choice.

It is understood to be 彼女, even though it is not repeated inside the clause.

Japanese often omits subjects when they are clear from context. So:

• 彼女は 終電に間に合うかどうか 心配していた

naturally means:

• She was worried about whether she would make the last train.

If you wanted to state it explicitly, you could say:

• 彼女は、彼女が終電に間に合うかどうか心配していた。

But that sounds repetitive, so Japanese normally leaves the second 彼女が out.

心配していた is the ている form in the past, and here it means was worried.

With many verbs of emotion or mental state, ている does not always mean a visible ongoing action like is doing. It often describes a continuing state.

So:

• 心配する = to worry
• 心配している = is worried / is worrying
• 心配していた = was worried / had been worrying

This gives a sense that her worry continued for some period of time, rather than being just a single momentary feeling.

Both can be translated as was worried, but the nuance is a little different.

• 心配だった describes a state or feeling more directly: was worried
• 心配していた emphasizes the ongoing act/state of worrying

So:

• 彼女は心配だった = She was worried.
• 彼女は心配していた = She was worrying / She was in a worried state.

In this sentence, 心配していた fits well because it sounds like she kept worrying about whether she would make the last train.

By itself, 遅延 just means delay, but in this sentence it strongly suggests a transportation delay, especially because 終電 is involved.

So a Japanese learner should notice that the sentence does not literally say train delay, but the context makes that interpretation very natural.

If someone wanted to be more explicit, they could say:

• 電車の遅延があって、... = because there was a train delay, ...

But the shorter 遅延があって is perfectly natural when the context already makes it clear.