kanozyo ha kidoku ga tuita noni, henzi ga konai to sukosi sinpai ni naru rasii.

A natural way to break it up is:

• 彼女は = as for her
• 既読がついたのに = even though it got marked as read
• 返事が来ないと = if/when no reply comes
• 少し心配になる = she gets a little worried
• らしい = apparently / it seems

So the sentence stacks several pieces together:

• a topic: 彼女は
• a contrast/background clause: 既読がついたのに
• a condition/trigger: 返事が来ないと
• the main result: 少し心配になる
• the speaker’s distance/uncertainty/hearsay marker: らしい

In smoother English, it is something like:

• Apparently, she gets a little worried when a message shows as read but no reply comes.

Because they are doing different jobs.

• 彼女は marks the topic of the whole sentence: we are talking about her.
• 既読が is the subject of the smaller clause 既読がついた.
• 返事が is the subject of the smaller clause 返事が来ない.

So this is a very common pattern in Japanese:

• Topic of whole sentence → は
• Subject inside a clause → often が

You can think of it like this:

• As for her,
  the read receipt appears, and the reply doesn’t come, so she gets worried.

Japanese often has one big sentence with smaller clauses inside it, and each clause can have its own が-marked subject.

既読 means read, in the sense of a message being marked as read in a messaging app.

つく literally has meanings like:

• to be attached
• to appear
• to get added
• to come on

So 既読がつく means something like:

• to get a read mark
• to show as read
• to be marked as read

It is a very natural expression in texting/app contexts.

Also, the thing that was read is omitted because it is obvious from context. Japanese often leaves out what English would explicitly say:

• メッセージに既読がつく = a message gets marked as read
• here just 既読がついた = it got marked as read

Because it refers to a change that has already happened:

• first, the message became read
• after that, no reply came
• then she got worried

So 既読がついた means the read mark appeared / got attached already.

In English, we might say:

• it shows as read
• it was marked as read
• the read receipt came on

Japanese often uses the past form when a state results from a completed event.

Here のに means even though, although, or despite that.

So:

• 既読がついたのに = even though it was marked as read

The nuance is that something feels unexpected or contrary to what you would normally expect.

The implied logic is:

• If someone has already read the message, you would expect a reply.
• But no reply comes.
• That gap creates worry.

So のに is stronger than a plain and. It adds a feeling of:

• but still
• and yet
• despite that

Yes. Here と is a conditional.

• 返事が来ないと = if no reply comes / when no reply comes

With と, the result often sounds like a natural, regular, or automatic consequence.

So in this sentence, the nuance is not a one-time hypothetical like:

• What if no reply comes?

It is more like:

• When that happens, she gets a little worried
• If that situation occurs, that is the result

That is why と works well here.

So:

• 返事が来ないと、少し心配になる = When no reply comes, she gets a little worried

Because 返事が来る is a very natural way to say a reply comes or I get a reply.

So:

• 返事が来ない = no reply comes / I don’t get a reply

This focuses on the reply not arriving.

Compare:

• 返事が来ない
  = no reply comes / no reply is received

• 返事しない
  = someone does not reply

• 返事がない
  = there is no reply

All are possible in some contexts, but they feel slightly different.

Here 返事が来ない is especially natural because the speaker is describing the experience from the receiver’s side: the reply simply does not arrive.

心配になる means to become worried.

Here, 心配 behaves like a na-adjective / adjectival noun, and with なる, that pattern is:

• A に なる = become A

So:

• 心配になる = become worried
• 元気になる = become well / lively
• 静かになる = become quiet

The に marks the state that someone changes into.

So in this sentence:

• 少し心配になる = to become a little worried

They are related, but not identical.

• 心配だ = to be worried
• 心配する = to worry
• 心配になる = to become worried

In this sentence, 心配になる is a good fit because it describes a change of feeling triggered by a situation:

• the message is read
• no reply comes
• then she starts to feel worried

If you used 心配だ, it would sound more like a static state:

• she is worried

If you used 心配する, it would focus a bit more on the act or tendency of worrying:

• she worries

So 心配になる nicely captures the moment or tendency of becoming worried when that situation happens.

少し means a little or somewhat.

So:

• 少し心配になる = get a little worried

It softens the statement. Without 少し, the sentence would sound stronger:

• 心配になる = gets worried

With 少し, it sounds more moderate and natural, like:

• she gets a bit worried
• she starts to worry a little

This kind of softening is very common in Japanese.

Here らしい means something like:

• apparently
• it seems
• I hear that
• it sounds like

It shows that the speaker is not stating the information as a direct, certain fact from their own inner knowledge.

That is especially useful here because the sentence talks about someone else’s feelings:

• 彼女は…心配になる

In Japanese, speakers often avoid sounding too certain about another person’s internal emotions unless they have some basis for it. So らしい makes the sentence more natural by adding distance:

• Apparently, she gets a little worried
• It seems she gets a little worried

Depending on context, らしい can be based on:

• what someone said
• what the speaker heard
• what the speaker inferred from evidence

Yes. They are doing different things.

• のに adds a contrast:
  even though it was read

• と gives the result-trigger relationship:
  when no reply comes, she gets worried

So the sentence is layering two ideas:

1. It was already read
2. and yet no reply comes
3. when that happens, she gets a little worried

Japanese often builds long sentences by connecting several clause types like this. It can feel dense at first, but once you identify each connector, the structure becomes much easier to follow.