אני יודעת לאיית את המילה הזאת, אבל קשה לי לזכור אם היא בזמן עבר או לא.

Because the speaker is female.

In Hebrew, present-tense verbs agree with the subject’s gender and number:

• אני יודע = I know (said by a man)
• אני יודעת = I know (said by a woman)

So יודעת tells you the speaker is feminine singular.

In modern Hebrew, the present tense is often built from forms that historically functioned like participles, but you should treat them as normal present-tense verb forms.

So:

• אני יודעת = I know
• אני לומדת = I study / I am studying
• אני כותבת = I write / I am writing

That is why יודעת works naturally for I know.

לאיית means to spell.

The prefix ל־ is the usual marker of the infinitive in Hebrew, so it often corresponds to English to:

• לזכור = to remember
• לכתוב = to write
• לאיית = to spell

After verbs like יודע / יודעת, Hebrew often uses an infinitive:

• אני יודעת לאיית = I know how to spell

Here, יודעת + infinitive means know how to do something.

Here את is the direct object marker.

Hebrew uses את before a direct object that is definite, such as:

• a noun with ה־
• a proper name
• a pronoun
• something like this/that when it is definite

So:

• לאיית את המילה הזאת = to spell this word

The את is not translated into English. It is just a grammatical marker.

Compare:

• אני קורא ספר = I am reading a book
• אני קורא את הספר = I am reading the book

In Hebrew, demonstratives like this usually come after the noun:

• המילה הזאת = this word
• הספר הזה = this book
• הילדה הזאת = this girl

So the normal order is:

noun + this/that

Also, the demonstrative has to agree with the noun:

• מילה is feminine singular
• so the form is הזאת

That is just how standard Hebrew normally forms this/that + noun:

• הספר הזה
• המילה הזאת
• הבית ההוא

The noun usually takes ה־, and the demonstrative comes after it.

So המילה הזאת is the normal way to say this word.

Literally, קשה לי means something like hard to me.

This is a very common Hebrew pattern:

• קשה לי = it is hard for me
• קל לי = it is easy for me
• חשוב לי = it is important to me

So Hebrew often expresses this kind of idea with:

adjective + ל־ + person

Then the action comes after it:

• קשה לי לזכור = it is hard for me to remember

Because לזכור is also an infinitive: to remember.

Hebrew commonly uses an infinitive after expressions like קשה לי:

• קשה לי להבין = it is hard for me to understand
• קל לי לקרוא = it is easy for me to read
• אסור לי להיכנס = I am not allowed to enter

So קשה לי לזכור is the normal structure for it’s hard for me to remember.

Here אם means whether.

Hebrew uses אם for indirect yes/no questions:

• אני לא יודע אם הוא בבית = I don’t know whether he is at home
• אני זוכרת אם זה נכון = I remember whether it is correct

So in this sentence:

• לזכור אם היא בזמן עבר או לא

the אם introduces the idea whether it is in the past tense or not.

It is not a conditional if here.

It refers back grammatically to המילה.

Since מילה is a feminine noun, the pronoun that refers to it is also feminine:

• מילה → היא

English would use it, but Hebrew uses gendered pronouns because nouns have grammatical gender.

So even though English says whether it is..., Hebrew says אם היא... because word is feminine.

Because בזמן עבר specifically means in the past tense in a grammatical sense.

• עבר by itself often means the past
• בזמן עבר makes it clear that we are talking about verb tense

So:

• הוא דיבר בעבר could mean something like he spoke in the past
• הוא בזמן עבר or זה בזמן עבר means it is in the past tense

In grammar talk, בזמן עבר is much clearer.

או לא means or not.

So:

• אם היא בזמן עבר = whether it is in the past tense
• אם היא בזמן עבר או לא = whether it is in the past tense or not

Hebrew often uses אם ... או לא to make the two possibilities explicit.

Literally, yes, the structure is close to I know to spell, but the natural meaning is I know how to spell.

With יודע / יודעת + infinitive, Hebrew often expresses ability or know-how:

• אני יודע לשחות = I know how to swim
• היא יודעת לבשל = she knows how to cook
• אני יודעת לאיית = I know how to spell

So this is a very useful pattern to learn.

Usually no, not in this kind of embedded clause.

• האם is commonly used to introduce a direct formal yes/no question
• אם is the normal choice inside a larger sentence after verbs like know, remember, ask, check

So Hebrew prefers:

• אני לא יודעת אם זה נכון

rather than:

• אני לא יודעת האם זה נכון

You may sometimes see האם in careful or formal writing, but אם is the most natural choice here.