У этой блузки шёлк очень тонкий, поэтому её лучше стирать вручную.

У этой блузки is a very common Russian way to talk about a feature, part, or property of something.

Literally, у этой блузки шёлк очень тонкий is something like:

• at this blouse, the silk is very thin

But in natural English, it means:

• This blouse has very thin silk
• The silk of this blouse is very thin

Russian often uses у + genitive to mean someone/something has something, especially when talking about:

• body parts
• qualities
• features
• materials
• characteristics

So here, Russian is focusing on the blouse as the item being described, and then saying what its silk is like.

Этой блузки is in the genitive case because it follows у.

The pattern is:

• у + genitive

So:

• эта блузка → nominative
• у этой блузки → genitive

This construction often expresses possession or association:

• У девушки длинные волосы. = The girl has long hair.
• У машины новый двигатель. = The car has a new engine.
• У этой блузки шёлк очень тонкий. = This blouse has very thin silk.

In the present tense, Russian usually does not use a verb equivalent to is/am/are.

So instead of saying something like the silk is very thin with a separate verb, Russian simply says:

• шёлк очень тонкий

Literally:

• silk very thin

which means:

• the silk is very thin

For possession, Russian also often avoids a direct verb like have and instead uses the у + genitive structure:

• У меня есть книга. = I have a book.
• У этой блузки шёлк очень тонкий. = This blouse has very thin silk.

So the sentence is completely normal even though there is no separate word for is or has.

Шёлк is the grammatical subject of the clause шёлк очень тонкий.

That part means:

• the silk is very thin

Since шёлк is the subject, it appears in the nominative singular.

You can think of the structure like this:

• У этой блузки = as for this blouse / this blouse has
• шёлк = the silk
• очень тонкий = is very thin

So even though English might think first of blouse as the main thing, grammatically in Russian the word шёлк is the subject of the description.

Because тонкий agrees with шёлк, and шёлк is:

• masculine
• singular
• nominative

So the adjective must also be:

• masculine singular nominative → тонкий

Compare:

• шёлк тонкий — masculine
• ткань тонкая — feminine
• полотно тонкое — neuter
• нитки тонкие — plural

It does not agree with блузки, because the adjective is describing шёлк, not the blouse.

Yes, тонок is possible, but тонкий is more neutral and common in everyday speech.

Compare:

• Шёлк очень тонкий. — standard, neutral
• Шёлк очень тонок. — more literary, formal, or stylistically marked

Russian has both full adjectives and short adjectives in predicate position. In many ordinary situations, learners will hear the full form more often:

• дом большой
• фильм интересный
• шёлк тонкий

The short form exists, but it can sound more bookish or stylistically special depending on the adjective.

Поэтому means therefore, that’s why, or so.

It connects the first idea to the result:

• У этой блузки шёлк очень тонкий, поэтому её лучше стирать вручную.

So the logic is:

1. the silk is very thin
2. therefore / so
3. it is better to wash it by hand

It often appears near the beginning of the second clause, just as it does here.

Other possible translations depending on style:

• therefore
• so
• for that reason
• that’s why

Here её is the accusative form, because it is the direct object of стирать.

The sentence means:

• it is better to wash it by hand

So её = it, referring back to блузку.

Since блузка is feminine singular, the corresponding pronoun is её.

Important point: in form, её can also be genitive, but here the function is clearly accusative because it is the thing being washed.

Лучше + infinitive is a very common Russian pattern meaning:

• it is better to do something
• better to do something

So:

• её лучше стирать вручную = it’s better to wash it by hand

This is an impersonal construction. Russian does not need to say it is explicitly.

Some similar examples:

• Лучше подождать. = It’s better to wait.
• Эту рубашку лучше гладить осторожно. = It’s better to iron this shirt carefully.
• Овощи лучше хранить в холодильнике. = Vegetables are better kept in the refrigerator / It’s better to store vegetables in the refrigerator.

This structure is especially common in advice, instructions, and recommendations.

Стирать is imperfective, and that is natural here because the sentence gives a general care instruction or recommendation, not a one-time completed action.

So:

• её лучше стирать вручную = it’s better to wash it by hand
  meaning whenever you wash it / as a general rule

Imperfective is commonly used for:

• general habits
• instructions
• repeated actions
• actions viewed as a process

A perfective form such as постирать would suggest a more specific, one-time action:

• Её лучше постирать вручную. = You’d better wash it by hand (this time / in this situation).

Both are possible in some contexts, but стирать is better for a label-like or general-care meaning.

Вручную means by hand.

So:

• стирать вручную = to wash by hand

It is an adverb, and in meaning it contrasts with washing something in a machine.

Examples:

• Мыть посуду вручную = to wash dishes by hand
• Шить вручную = to sew by hand
• Стирать вручную = to wash by hand

This is simply the normal word to use here.

Yes, absolutely.

• Эту блузку лучше стирать вручную. = This blouse is better washed by hand / It’s better to wash this blouse by hand.

That version is more direct and simpler.

The original sentence adds an explanation first:

• У этой блузки шёлк очень тонкий, поэтому её лучше стирать вручную.

So the original means:

1. the blouse has very thin silk
2. therefore hand washing is better

In other words, the first clause gives the reason for the recommendation.

Russian often uses a pronoun once the noun is already clear from context, just like English.

So after mentioning этой блузки, it is natural to continue with:

• её лучше стирать вручную

instead of repeating:

• эту блузку лучше стирать вручную

Both are correct, but using её sounds smoother and avoids repetition.

The word order is natural, but Russian word order is more flexible than English.

The sentence is arranged like this:

• У этой блузки — sets the topic: this blouse
• шёлк очень тонкий — gives the description
• поэтому — connects cause and result
• её лучше стирать вручную — gives the recommendation

This order sounds logical and smooth:

1. mention the item
2. describe the problem or characteristic
3. give the consequence

Russian could rearrange parts for emphasis, but the version you have is very standard and easy to understand.