היא קונה לעצמה שמלה חדשה.

Yes, Hebrew can sometimes leave out the subject if it is clear from context, but in the present tense the verb usually does not show person clearly the way English does.

So היא helps make it explicit that the subject is she.

Without היא, קונה by itself could mean something like buys / is buying, but you would need context to know who is doing it.

It can mean either one.

Hebrew present tense often covers both:

• she buys
• she is buying

Context tells you which is more natural in English.

Not in this case.

With the verb לקנות in the present singular, קונה can be used for both:

• הוא קונה = he buys / is buying
• היא קונה = she buys / is buying

So here, the word היא is what tells you the subject is feminine.

The dictionary form is לקנות, meaning to buy.

So:

• לקנות = to buy
• קונה = buying / buys

לעצמה means for herself or to herself, depending on context. In this sentence it gives the idea for herself.

It shows that the action is reflexive in sense: she is buying the dress for her own benefit.

So the structure is roughly:

• היא קונה = she is buying
• לעצמה = for herself
• שמלה חדשה = a new dress

Because לה usually means to her / for her, and it does not automatically mean that her is the same person as the subject.

Compare:

• היא קונה לה שמלה can sound more ambiguous or colloquial
• היא קונה לעצמה שמלה clearly means she is buying herself a dress

So לעצמה makes the reflexive meaning very clear: the buyer and the beneficiary are the same person.

Yes, it is written as one word.

It is made from:

• ל־ = to / for
• עצמה = herself

Together: לעצמה = for herself

This is part of a common Hebrew pattern with עצמי / עצמך / עצמו / עצמה and so on:

• לעצמי = for myself
• לעצמך = for yourself
• לעצמו = for himself
• לעצמה = for herself

Because Hebrew has no indefinite article.

So Hebrew does not have a separate word for a/an.

That means:

• שמלה חדשה = a new dress

If you wanted the new dress, Hebrew would say:

• השמלה החדשה

Because את marks a definite direct object, and שמלה חדשה here is indefinite: a new dress, not the new dress.

So:

• היא קונה לעצמה שמלה חדשה = no את, because the object is indefinite
• היא קונה לעצמה את השמלה החדשה = with את, because the object is definite

Because in Hebrew, adjectives normally come after the noun.

So:

• שמלה חדשה = a new dress

This is the normal order in Hebrew:

• noun + adjective

Because שמלה is feminine singular, and the adjective must agree with it.

So:

• שמלה = feminine singular
• חדשה = feminine singular form of new

Compare:

• בגד חדש = a new garment/clothing item
• שמלה חדשה = a new dress

You mainly learn the noun's gender as part of the word, but there are clues.

One clue is the ending ־ה, which often marks feminine nouns. Also, the adjective agrees with it:

• שמלה חדשה

That חדשה confirms that שמלה is being treated as feminine.

Yes, Hebrew word order is somewhat flexible.

You could also hear:

• היא קונה שמלה חדשה לעצמה

That still means She is buying herself a new dress.

The original order,

• היא קונה לעצמה שמלה חדשה is very natural and puts לעצמה early, which can slightly highlight for herself.

You would make the object definite:

היא קונה לעצמה את השמלה החדשה.

Notice two things:

• את appears because the direct object is definite
• both the noun and adjective get ה־:
  • השמלה
  • החדשה