אני יודעת שזאת לא רק דעה אלא עובדה, ואם יש לך מידע רלוונטי נוסף, תשלחי לי אותו.

Because יודעת is the feminine singular form of know in the present tense.

• אני יודע = I know said by a male speaker
• אני יודעת = I know said by a female speaker

Hebrew present-tense verbs agree with the gender and number of the subject, even with אני.

זאת means this in the feminine singular.

In this sentence, it appears in שזאת לא רק דעה אלא עובדה = that this is not just an opinion but a fact.

A learner may expect זה, but זאת/זו is feminine, and it fits well here because both דעה and עובדה are feminine nouns.

Also, in modern Hebrew:

• זו is very common
• זאת is also common and slightly fuller-sounding

So שזאת and שזו are both natural in many contexts.

ש־ is a very common Hebrew particle meaning that.

So:

• אני יודעת ש... = I know that...

Here, שזאת is really:

• ש + זאת = that + this

Hebrew often attaches ש־ directly to the following word.

This is a fixed pattern meaning not only / not just ... but ...

In your sentence:

• לא רק דעה אלא עובדה
• literally: not only an opinion but a fact
• natural English: not just an opinion, but a fact

A very common expanded version is:

• לא רק ... אלא גם ... = not only ... but also ...

But in this sentence, גם is not necessary.

Because Hebrew has no indefinite article.

So:

• דעה can mean an opinion
• עובדה can mean a fact

Hebrew only marks the definite article:

• הדעה = the opinion
• העובדה = the fact

In this sentence, the meaning is indefinite/general, so no ה־ is used.

Hebrew usually expresses possession with יש ל־..., literally something like there is to...

So:

• יש לך מידע = literally there is to you information
• natural English: you have information

This is the normal Hebrew way to say have in many contexts.

Examples:

• יש לי שאלה = I have a question
• יש להם זמן = they have time

This means additional relevant information.

A few useful things are happening here:

1. מידע = information
2. Hebrew adjectives usually come after the noun
3. Adjectives must agree with the noun in gender and number

So:

• מידע = masculine singular
• רלוונטי = masculine singular adjective, relevant
• נוסף = masculine singular adjective, additional/further

Word order:

• מידע רלוונטי נוסף
• literally: information relevant additional
• natural English: additional relevant information

Because אותו agrees with the grammatical gender of מידע, and מידע is masculine singular in Hebrew.

So:

• אותו = him/it for a masculine singular noun
• here it means it

In the sentence, אותו refers back to מידע.

Compare:

• ספר (book, masculine) → אותו
• שאלה (question, feminine) → אותה

So if the noun were feminine, the sentence would use אותה instead.

תשלחי is the second person feminine singular form, so the speaker is addressing one female person.

The rest breaks down like this:

• תשלחי = you will send / send
• לי = to me
• אותו = it

So literally:

• send to me it

Natural English:

• send it to me

Hebrew commonly puts the indirect object first here:

• תשלחי לי אותו = send it to me

That word order is very natural.

Grammatically, תשלחי is the future tense form: you (feminine singular) will send.

But in real Hebrew, future forms are often used to give instructions, requests, or commands, especially in a softer or less abrupt way.

So here:

• אם יש לך מידע רלוונטי נוסף, תשלחי לי אותו
• literally: if you have additional relevant information, you will send it to me
• actual meaning: if you have any additional relevant information, send it to me

A more direct imperative would be:

• שלחי לי אותו

Using the future here sounds natural and slightly softer.

Hebrew often marks gender in the second person.

In this sentence, the speaker is talking to one female:

• יש לך can be used for both masculine and feminine in everyday writing, since לך is written the same either way
• תשלחי clearly shows feminine singular

If the speaker were addressing a male, you would say:

• ואם יש לך מידע רלוונטי נוסף, תשלח לי אותו

So the sentence tells us:

• the speaker is female: אני יודעת
• the person being addressed is female: תשלחי

זו could often replace זאת here:

• אני יודעת שזו לא רק דעה אלא עובדה

That would sound very natural.

But זה would change the feel, because זה is masculine. Native speakers sometimes use זה very broadly in speech, but in a sentence like this, זו/זאת fits better because the nouns involved, דעה and עובדה, are feminine.

So:

• שזו... = very natural
• שזאת... = also natural
• שזה... = possible in some speech patterns, but less fitting here for a learner to imitate