Другая таможенница только улыбнулась и сказала, что штамп уже стоит.

Because другая has to agree with таможенница in:

• gender: feminine
• number: singular
• case: nominative

Таможенница is a feminine noun, so the adjective must also be feminine: другая.

Here it means the other customs woman / another customs officer.

Таможенница means female customs officer or customs woman.

It is the feminine form of:

• таможенник = male customs officer
• таможенница = female customs officer

Russian often has masculine and feminine versions of nouns for professions or roles, especially when talking about a specific person.

It can feel like either the other or another, depending on context.

In this sentence, другая таможенница most naturally means:

• the other customs officer if two officers are being contrasted
• another customs officer if one officer has already been mentioned and now the speaker refers to a different one

Russian другой / другая / другое covers both ideas more broadly than English sometimes does.

Here только means only, but in a very natural conversational sense:

• только улыбнулась = just smiled / only smiled

The idea is that she did not argue, explain much, or react strongly. She simply smiled.

So it adds a nuance like:

• all she did was smile
• she just smiled

The verb is улыбнуться = to smile.

The -ся / -сь ending is the reflexive marker. In this verb, it is just part of the normal dictionary form; you do not translate it literally as oneself in English.

So:

• улыбнуться = to smile
• улыбнулась = she smiled

Grammatically, улыбнулась is:

• past tense
• feminine singular
• perfective

The feminine ending is -а in the past, but because the verb ends in -сь, you see улыбнулась.

Because the subject is таможенница, which is feminine singular.

In the Russian past tense, verbs agree with the subject in gender and number:

• он сказал = he said
• она сказала = she said
• она улыбнулась = she smiled

So both verbs match the same female subject:

• другая таможенница только улыбнулась и сказала...

Russian often omits repeated pronouns, so after the noun is stated once, there is no need to repeat она.

Because Russian often leaves out subject pronouns when the subject is already clear.

In English, you normally say:

• The other customs officer just smiled and said...

You do not need to repeat she there either. Russian works similarly.

So:

• Другая таможенница только улыбнулась и сказала...

is completely natural, and the subject of both verbs is clearly the same person.

Что here means that and introduces reported speech or an indirect statement.

So:

• сказала, что... = said that...

This is one of the most common patterns in Russian:

• Он сказал, что устал. = He said that he was tired.
• Она сказала, что всё готово. = She said that everything was ready.

In everyday English, that is often omitted, but in Russian что is normally kept.

This is a very important point.

...сказала, что штамп уже стоит literally means something like:

• ...said that the stamp is already there
• ...said that the stamp has already been put on

Russian does not backshift tenses as automatically as English often does.

In English, after a past verb like said, you often expect:

• said that the stamp was already there

But Russian can keep the present tense if the statement was true at that moment in the reported situation:

• сказала, что штамп уже стоит

So Russian is describing what she said from her point of view at that time: the stamp is already on it.

Literally, стоит means stands. But here it is idiomatic.

With things like stamps, signatures, labels, or marks, Russian often uses стоять to mean:

• to be there
• to be present
• to appear on something
• to have already been placed

So:

• штамп стоит = the stamp is on it
• штамп уже стоит = the stamp is already there / has already been stamped

This is a very common Russian way of speaking.

Related expression:

• поставить штамп = to put/stamp a stamp on a document

So the sentence implies that the document already had the necessary stamp.

Уже means already, and it usually goes before the word or phrase it is emphasizing.

Here:

• штамп уже стоит

means:

• the stamp is already there

This is the most neutral and natural word order.

You may see other orders in Russian for emphasis, but this one is standard and straightforward.

The word order is quite natural and neutral.

• Другая таможенница = the subject
• только улыбнулась и сказала = the two actions
• что штамп уже стоит = what she said

Russian word order is more flexible than English, but this sentence is arranged in a very normal storytelling order:

1. who did it
2. what she did
3. what she said

So for a learner, this is a good example of standard Russian sentence structure.

Yes, there is a difference.

• улыбнулась = smiled as a completed single action
• улыбалась = was smiling / smiled repeatedly / smiled for some time

In this sentence, улыбнулась fits because it describes one brief reaction:

• she smiled
• then she said something

So the perfective verb gives the sense of a single completed event in the story sequence.