Дочка открыла гуашь и нечаянно испачкала рукав.

Дочка is a more affectionate, everyday form of дочь (daughter).

• дочь = the basic dictionary form, a bit more formal or neutral
• дочка = very common in normal speech, warmer and more natural in many contexts

So this sentence sounds like natural everyday Russian.

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

The subject is дочка, which is:

• singular
• feminine

So the past-tense verbs take the feminine singular form:

• открыл = he opened

• открыла = she opened

• испачкал = he stained/made dirty
• испачкала = she stained/made dirty

That -ла ending is a very common sign of feminine past tense.

Both are perfective verbs.

• открыла = opened (completed action)
• испачкала = stained/got dirty (result happened)

Perfective is used because the sentence describes two finished actions with clear results:

1. she opened the paint
2. she got the sleeve dirty

If you used imperfective, the focus would be more on the process, repetition, or background action rather than the completed result.

Гуашь is in the accusative case here because it is the direct object of открыла.

But for this noun, the accusative singular looks the same as the nominative singular:

• nominative: гуашь
• accusative: гуашь

This is normal for many inanimate feminine nouns, especially ones ending in -ь.

So even though the case changed grammatically, the form stayed the same.

Рукав is also in the accusative case, because it is the thing that got stained.

However, рукав is:

• masculine
• singular
• inanimate

For masculine inanimate nouns, the accusative singular is usually identical to the nominative singular:

• nominative: рукав
• accusative: рукав

So the form does not change.

Russian often leaves out possessive words when the owner is obvious from context.

In English, you often say:

• She stained her sleeve

In Russian, it is very natural to say simply:

• испачкала рукав

because it is clear that the sleeve belongs to the girl.

If needed for emphasis or clarity, Russian could say:

• испачкала свой рукав = stained her own sleeve

But in this sentence, that would sound less natural unless there were a special reason to stress it.

Нечаянно means accidentally, unintentionally, or without meaning to.

It emphasizes that the action was not deliberate.

So:

• нечаянно испачкала рукав = she accidentally got the sleeve dirty

A close word is случайно, which can also mean accidentally. In many contexts they overlap, but нечаянно often has a slightly more personal sense of not meaning to.

In Russian, if the same subject does both actions, it is very normal to mention the subject once and then give multiple verbs:

• Дочка открыла гуашь и нечаянно испачкала рукав.

This means:

• the girl opened the gouache
• and the girl accidentally stained the sleeve

Russian does not need to repeat дочка the second time.

Yes. Russian word order is flexible, though different orders can sound more natural in different contexts.

The original order is very neutral:

• Дочка открыла гуашь и нечаянно испачкала рукав.

You could also say:

• Нечаянно дочка открыла гуашь и испачкала рукав.
• Дочка нечаянно открыла гуашь и испачкала рукав.

But these can shift the focus slightly.

In the original sentence, нечаянно most naturally goes with испачкала, so it sounds like:

• she opened the paint, and then accidentally stained the sleeve

It is pronounced approximately goo-AHSHʹ.

Stress: гуа́шь

The final ь is the soft sign. It does not make its own sound, but it softens the preceding consonant. So ш is made a little softer than it would be without the soft sign.

For a learner, the key thing is:

• stress on а
• final шь is a soft ending

Yes. In Russian, you can open a container or substance by referring just to the substance itself, especially in everyday speech.

So открыла гуашь naturally means something like:

• opened the gouache paint
• opened the container of gouache

Russian often leaves out the container if it is obvious.

Russian often uses и simply to connect actions, and the sequence is understood from logic and context.

Here the most natural reading is:

1. she opened the gouache
2. as a result, she accidentally stained the sleeve

You do not need a separate word like then unless you want extra emphasis. Russian commonly relies on context for this kind of sequencing.