אני מתגעגעת לאחותי כשהיא לא בבית כמה ימים.

Because the speaker is female. In the present tense, Hebrew verbs agree with gender and number.

• אני מתגעגעת = I miss / I am missing said by a woman
• אני מתגעגע = the same thing said by a man

So this sentence tells you that the speaker is feminine.

In this sentence, אני is helpful and usually expected.

Unlike past and future tense, Hebrew present-tense verb forms do not clearly show person. מתגעגעת could mean:

• I miss
• you miss (feminine singular)
• she misses

So אני makes it clear that the meaning is I miss. Without it, the sentence would sound incomplete or ambiguous unless the context already made the subject obvious.

Because the verb להתגעגע works with the preposition ל־.

In English, we say miss someone with a direct object. In Hebrew, the structure is different:

• אני מתגעגעת לאחותי
• literally: I long/miss to my sister

So after מתגעגע/ת, you normally use ל־ before the person or thing you miss.

That means:

• לאחותי = to my sister / for my sister
• את אחותי would be incorrect with this verb

Hebrew often adds possessive endings directly to nouns.

• אחות = sister
• אחותי = my sister

The ending ־י means my.

Some similar examples:

• אחי = my brother
• אמא שלי = my mom
• ספרי = my book

So לאחותי breaks down as:

• ל־ = to / for
• אחותי = my sister

כשהיא means when she.

It is made from:

• כש־ = when
• היא = she

In Hebrew, short connecting words are often attached directly to the following word, so כשהיא is completely normal.

You may also see the fuller form כאשר היא, but כשהיא is much more natural in everyday speech.

Because in Hebrew, the verb to be is usually omitted in the present tense.

So:

• היא בבית = she is at home
• היא לא בבית = she is not at home

Hebrew does use forms of to be in past and future:

• היא הייתה בבית = she was at home
• היא תהיה בבית = she will be at home

But in the present, no separate word for is is normally used.

Here, בבית means at home.

It comes from:

• ב־ = in / at
• בית = house / home

So literally it is in the house/home, but in many contexts it naturally means at home.

In this sentence, היא לא בבית is best understood as she isn’t at home.

Hebrew often expresses duration without adding a special word like for.

So:

• כמה ימים = a few days
• in context, לא בבית כמה ימים = not at home for a few days

This is very normal. Hebrew often uses a bare time expression to show how long something lasts.

If you wanted to be more explicit, you could also say:

• במשך כמה ימים = for a few days
• כבר כמה ימים = already for a few days

It describes the absence, not the missing.

So the idea is:

• I miss my sister when she is not at home for a few days

In other words, the phrase כמה ימים goes with היא לא בבית.

A learner might wonder whether it could mean I miss my sister for a few days, but that is not the natural reading here. The intended meaning is that her being away lasts a few days.

Yes. The verb form is present tense, but Hebrew present tense can also express a habitual or general situation.

So אני מתגעגעת לאחותי כשהיא לא בבית כמה ימים can mean something like:

• I miss my sister when she’s away from home for a few days
• Whenever she isn’t home for a few days, I miss her

This is similar to English present tense in sentences like I get worried when he is late.

Yes, it is understandable and basically natural. A native speaker might sometimes add a word such as כבר to make the time phrase sound a little smoother:

• אני מתגעגעת לאחותי כשהיא לא בבית כבר כמה ימים

That gives the sense of when she has already been away from home for a few days.

But the original sentence is still clear and grammatical for a learner to study.