הייתי צריכה לשלוח לדוד ולדודה שלה הזמנה חדשה, כי יש להם כתובת חדשה.

הייתי צריכה literally means I was needing, but in Hebrew this is a very common way to say I needed to or I had to in the past.

• אני צריכה = I need to / I need
• הייתי צריכה = I needed to / I had to

So:

• הייתי צריכה לשלוח = I had to send / I needed to send

Also, צריכה is feminine singular, so this tells you the speaker is female. A male speaker would say:

• הייתי צריך לשלוח

Because Hebrew adjectives and participle-like forms agree with the speaker’s gender.

Here, צריכה agrees with the implied subject I:

• female speaker: הייתי צריכה
• male speaker: הייתי צריך

This is very normal in Hebrew. Even when English uses the same form (I needed), Hebrew often shows whether the speaker is male or female.

לשלוח is the infinitive, meaning to send.

The ל־ at the beginning is the normal marker used in Hebrew infinitives:

• לכתוב = to write
• ללכת = to go
• לשלוח = to send

So in הייתי צריכה לשלוח, the structure is:

• הייתי צריכה = I had to
• לשלוח = send / to send

Together: I had to send

Because these are the people receiving the invitation, so Hebrew uses ל־ meaning to.

• לדוד = to David / to an uncle
• ולדודה שלה = and to her aunt

With send, Hebrew often marks the recipient with ל־, just like English uses to:

• שלחתי מכתב לדני = I sent a letter to Danny

So:

• לשלוח לדוד ולדודה שלה הזמנה חדשה = to send David and her aunt a new invitation

Because את is used before a definite direct object, and הזמנה חדשה here is indefinite.

Compare:

• שלחתי הזמנה = I sent an invitation
• שלחתי את ההזמנה = I sent the invitation

In your sentence:

• הזמנה חדשה = a new invitation

Since it is not the invitation, Hebrew does not use את.

Because in Hebrew, adjectives usually come after the noun.

So:

• הזמנה חדשה = a new invitation
• כתובת חדשה = a new address

This is the normal Hebrew word order for noun + adjective.

Also, חדשה is feminine singular, agreeing with the feminine singular nouns:

• הזמנה is feminine
• כתובת is feminine

In Hebrew, adjectives must agree with the noun in gender and number.

Here are the relevant words:

• הזמנה = invitation, feminine singular
• כתובת = address, feminine singular

So the adjective must also be feminine singular:

• חדשה = new (feminine singular)

That is why both phrases are:

• הזמנה חדשה
• כתובת חדשה

If the noun were masculine singular, you would usually get חדש instead.

שלה means her or literally of her.

So:

• דודה שלה = her aunt

Hebrew often shows possession with של:

• הספר שלה = her book
• הדודה שלה = her aunt

In your sentence, שלה refers to some female person already known from the context.

Because they are doing two different jobs.

• שלה = her
  This modifies דודה and tells you whose aunt it is: her aunt.

• להם = they have / to them
  Here it refers to David and her aunt together.

So:

• ולדודה שלה = and her aunt
• יש להם כתובת חדשה = they have a new address

Since David + her aunt is a mixed or unspecified-gender plural group, Hebrew normally uses the masculine plural form:

• להם = to them / they have

Hebrew does not usually use a normal verb for to have in the present tense. Instead, it uses יש plus a pronoun or noun.

So:

• יש לי = I have
• יש לך = you have
• יש להם = they have

Literally, it is something like there is to them, but the natural translation is simply they have.

So:

• כי יש להם כתובת חדשה = because they have a new address

Because Hebrew normally uses the masculine plural for mixed groups.

The group here is:

• דוד
  • דודה שלה

If דוד is a man named David, then the pair includes a male and a female, so Hebrew uses masculine plural:

• להם = to them / they have

If the group were entirely female, you would expect להן instead.

It can mean either, depending on context.

• דוד can be the name David
• דוד can also mean uncle

Without context, the sentence is ambiguous.

So לדוד ולדודה שלה could mean either:

• to David and her aunt or
• to an uncle and her aunt

In real life, context or vowel marking would usually make the intended meaning clearer. If the meaning has already been given to the learner, that is the interpretation to follow.

Because כי means because, and it introduces a reason clause.

The sentence has two parts:

• הייתי צריכה לשלוח לדוד ולדודה שלה הזמנה חדשה
• כי יש להם כתובת חדשה

The second part explains the reason for the first:

• I had to send ... a new invitation
• because they have a new address

The comma is common and helps separate the main statement from the explanation.

Not always, but very often it means because.

In this sentence, כי clearly introduces the reason:

• כי יש להם כתובת חדשה = because they have a new address

In other contexts, כי can sometimes mean that, especially after verbs of saying, knowing, or thinking. But here because is the natural meaning.

The sentence follows a very common Hebrew pattern:

• הייתי צריכה = I had to
• לשלוח = send
• לדוד ולדודה שלה = to David and her aunt
• הזמנה חדשה = a new invitation
• כי יש להם כתובת חדשה = because they have a new address

So the order is roughly:

subject + had to + infinitive + recipient + object + reason

English might sometimes place things a little differently, but this Hebrew order is perfectly natural.