musume ha mise de mita akai kaban wo mada hosigatte iru.

は marks 娘 as the topic: the sentence is talking about the daughter and then says something about her.

So the structure is roughly:

• 娘は = as for the daughter
• 店で見た赤いかばんをまだ欲しがっている = she still wants the red bag she saw at the store

If you used が instead, the sentence would feel more like you are specifically identifying the daughter as the one who wants it, often in contrast to someone else or as new information.

In many ordinary contexts, は is the natural choice here.

In Japanese, family terms like 娘, 母, 父, and so on are often used without 私の when the relationship is clear from context.

So 娘は often naturally means:

• my daughter in normal conversation

Japanese often leaves out information that can be easily understood. Adding 私の娘は is possible, but it is usually unnecessary unless you want to be especially clear or contrastive.

This is how Japanese relative clauses work.

In English, you might say:

• the red bag that she saw at the store

In Japanese, the whole descriptive part comes before the noun:

• 店で見た赤いかばん

So 店で見た directly modifies かばん.

Japanese does not use a word like that here. Instead, it simply puts the clause before the noun.

The most natural reading is:

• the red bag that she saw at the store

Here, 店で見た modifies かばん, and 赤い also modifies かばん.

So the noun かばん is being described in two ways:

• it is red
• it is the one seen at the store

Japanese stacks modifiers before the noun very naturally.

で marks the place where an action happens.

Since 見た is an action, 店で見た means:

• saw it at the store

So:

• 店で = at the store, as the location of the action
• 店に would usually suggest direction or existence, not the place where the act of seeing happened

That is why で is the correct particle here.

赤い is an い-adjective. It directly modifies a noun in its plain form:

• 赤いかばん = a red bag

Only な-adjectives use な before nouns. For example:

• 静かな店 = a quiet store

But 赤い is not a な-adjective, so 赤なかばん would be incorrect.

を marks the direct object of the verb.

The verb phrase here is 欲しがっている, so the thing being wanted is:

• 赤いかばんを

In other words, the bag is the object of the wanting.

A simple breakdown is:

• 娘は = the daughter
• 赤いかばんを = the red bag
• 欲しがっている = is showing that she wants / wants

This is a very common question.

欲しい is used to express the speaker’s own desire, or a desire very closely associated with the speaker in certain contexts.

But when talking about a third person’s desire, Japanese often uses 欲しがる instead.

So:

• 私はかばんが欲しい = I want a bag
• 娘はかばんを欲しがっている = my daughter wants a bag / is showing that she wants a bag

The idea behind 欲しがる is that the speaker is describing an observable sign of desire in someone else.

So this sentence is not just a mechanical grammar choice; it reflects a common Japanese tendency not to state another person’s inner feelings too directly.

〜ている here shows an ongoing state.

So 欲しがっている means something like:

• is wanting
• still wants
• has been wanting

It suggests that this is not just a momentary reaction. The daughter continues to want that bag.

In this sentence, that ongoing sense works especially well with まだ.

Here まだ means still.

So the nuance is:

• she still wants that red bag

It shows that this desire continues from an earlier time up to now.

This is different from the other common use of まだ, which can mean not yet when used with a negative sentence.

For example:

• まだ食べている = still eating
• まだ食べていない = not eaten yet

In your sentence, because the verb is not negative, まだ means still.

Because 見た is inside a modifier clause describing the bag, not the main verb of the whole sentence.

Japanese relative clauses keep whatever tense makes sense inside that clause.

So:

• 店で見たかばん = the bag that was seen at the store

The daughter saw the bag in the past, and now she still wants it. Those two time references are perfectly compatible:

• past event: 見た
• current ongoing state: 欲しがっている

It is understood from context, and the most natural subject is the daughter.

So the sentence is naturally understood as:

• the daughter still wants the red bag that she saw at the store

Japanese relative clauses often omit the subject when it is clear.

There is no explicit 娘が before 見た, but the sentence strongly suggests that the daughter is the one who saw the bag.

Japanese allows multiple modifiers before a noun, and the order can affect naturalness and clarity.

Here:

• 店で見た = seen at the store
• 赤い = red
• かばん = bag

So 店で見た赤いかばん is a natural way to pile up the descriptions before the noun.

It means:

• the red bag seen at the store

In practice, Japanese often places longer, clause-like modifiers first and shorter adjective modifiers closer to the noun, which is exactly what happens here. So this word order sounds very natural.