העברית שלה נשמעת טבעית יותר ויותר, כי היא מדברת עם ישראלים בכל יום.

The ה- makes עברית definite: העברית שלה = her Hebrew / the Hebrew she speaks.

In Hebrew, when possession is expressed with של, the noun is often marked as definite if the whole phrase is specific. So:

• העברית שלה = her Hebrew
• הספר שלה = her book

Without ה-, the phrase can sound less definite or less natural in this context.

Because Hebrew often uses the pattern:

noun + של + possessor

So העברית שלה is literally the Hebrew of her.

This is different from English, which usually puts the possessor first: her Hebrew.

A few more examples:

• החבר שלו = his friend
• הבית שלהם = their house

נשמעת literally means is heard, but in everyday Hebrew it often means sounds.

So:

• העברית שלה נשמעת טבעית = Her Hebrew sounds natural

It comes from the root ש-מ-ע, related to hearing.

Because העברית is a feminine singular noun, and the present-tense verb form agrees with it in gender and number.

So:

• feminine singular: נשמעת
• masculine singular: נשמע

Since the subject is העברית, you need נשמעת.

טבעית is feminine singular, so it matches העברית.

• טבעי = masculine singular
• טבעית = feminine singular

It is not הטבעית because this adjective comes after a verb and works as a predicate adjective: sounds natural. In that position, Hebrew does not usually add ה-.

So:

• העברית שלה נשמעת טבעית = correct
• העברית שלה נשמעת הטבעית = incorrect

יותר ויותר means more and more.

So:

• טבעית יותר ויותר = more and more natural

It is a very common Hebrew expression for gradual change:

• קשה יותר ויותר = more and more difficult
• חשוב יותר ויותר = more and more important

Hebrew can place יותר ויותר after the adjective, as in this sentence:

• טבעית יותר ויותר

This is natural and means more and more natural.

You may also see יותר ויותר טבעית in other contexts. Hebrew word order is often a bit more flexible than English here. The main thing is that יותר ויותר is modifying טבעית.

In the present tense, Hebrew verbs do not clearly mark person the way English does. מדברת can mean:

• she speaks
• you (feminine singular) speak
• or just speaking, depending on context

So adding היא makes the subject clear:

• כי היא מדברת = because she speaks / because she talks

It can mean either one, depending on context.

Hebrew present tense often covers both:

• an ongoing action: is speaking
• a habitual action: speaks

Here, because of בכל יום (every day), the meaning is habitual:

• כי היא מדברת עם ישראלים בכל יום = because she speaks with Israelis every day

The verb לדבר often goes with עם, meaning with:

• לדבר עם מישהו = to speak/talk with someone

So:

• מדברת עם ישראלים = she speaks with Israelis

Also, ישראלים has no ה-, so it means Israelis in general, not a specific group.

Compare:

• עם ישראלים = with Israelis
• עם הישראלים = with the Israelis

בכל יום means every day.

Literally, it is something like on every day or in every day, but the natural English translation is simply every day.

In everyday Hebrew, כל יום is also very common and often means the same thing. Very roughly:

• כל יום = common, everyday speech
• בכל יום = also correct, sometimes a bit more formal or emphatic

Here כי means because.

It introduces the reason:

• העברית שלה נשמעת טבעית יותר ויותר, כי היא מדברת עם ישראלים בכל יום.
• Her Hebrew sounds more and more natural, because she speaks with Israelis every day.

In some formal or literary Hebrew, כי can also mean that, but in this sentence it clearly means because.