kanozyo ha maiasa yotei wo tetyou ni kakikonde iru. dakara wasuremono ga sukunai wake da.

は marks 彼女 as the topic of the sentence.

So 彼女は means something like as for her or she in the sense of speaking about her.

This is very common in Japanese:

• 彼女は毎朝予定を書き込んでいる。 = As for her, she writes her plans down every morning.

If you used が instead, it would sound more like you are specifically identifying her as the person doing it, rather than simply introducing her as the topic.

毎朝 means every morning.

It is a time expression, and time expressions in Japanese are often placed near the beginning of the sentence, before the main action:

• 彼女は毎朝予定を書き込んでいる。

That word order is very natural.

You could think of the sentence as:

• As for her, every morning, she writes her plans into her planner.

Japanese word order is flexible, but placing 毎朝 before the object and verb is very standard.

This is about particles and what role each noun plays.

• 予定を: を marks the direct object, the thing being written.
• 手帳に: に marks the place or target where the writing goes.

So:

• 予定を書く = write plans
• 手帳に書く = write in a planner
• 予定を手帳に書き込む = write plans into a planner

A natural way to understand it is:

• 予定 = the content
• 手帳 = the destination/location for that content

That is why the particles are different.

書く just means to write.

書き込む adds the nuance of writing something into a space, entering it, or filling it in.

So in this sentence, 書き込む suggests that she is not just casually writing, but specifically entering her plans into her planner.

Compare:

• ノートに書く = write in a notebook
• 予定表に書き込む = write/fill plans into a schedule book

So 書き込む feels a little more specific and practical than plain 書く.

〜ている has several uses, and here it shows a habitual or ongoing repeated action.

So 書き込んでいる here does not necessarily mean she is writing right this second. It means something like:

• she regularly writes them down
• she has the habit of writing them down

Because the sentence also includes 毎朝, the habitual meaning is very clear.

So:

• 書き込む = writes / will write
• 毎朝書き込んでいる = is in the habit of writing every morning

This is a very common use of 〜ている in Japanese.

だから means so, therefore, or that’s why.

It connects the first sentence to the conclusion in the second:

• She writes her plans in her planner every morning.
• Therefore, she forgets things less often.

So the overall flow is:

1. cause/reason
2. result/conclusion

It is a very natural conversational connector.

忘れ物 means something forgotten, forgotten item, or things you forgot to bring.

In this sentence, it refers to forgotten belongings or items, like leaving something behind or forgetting to bring something.

Japanese nouns usually do not mark singular vs. plural clearly, so 忘れ物 can mean:

• a forgotten item
• forgotten items
• forgetting things

Here, the English meaning is probably best understood as she forgets things less often or she has fewer forgotten items.

Because 少ない is an adjective, not an action verb.

With adjectives like 多い and 少ない, the thing being described often takes が:

• 人が多い = there are many people
• ミスが少ない = there are few mistakes
• 忘れ物が少ない = there are few forgotten items / she forgets things less often

So が marks what is few.

Using を would not work here because 少ない is not something that directly acts on an object.

わけだ means something like:

• that explains why
• no wonder
• it follows that
• so that’s the reason

In this sentence:

• だから忘れ物が少ないわけだ。

The speaker is drawing a natural conclusion from the first sentence:

• She writes her plans down every morning.
• That’s why she forgets things less often.

So わけだ adds a nuance of logical conclusion or explanation, not just simple fact.

It is a little more thoughtful than just saying:

• だから忘れ物が少ない。

With わけだ, the speaker sounds like they are recognizing the reason behind it.

だ is the plain style copula, while です is more polite.

So:

• 忘れ物が少ないわけだ。 = plain style
• 忘れ物が少ないわけです。 = polite style

The plain style is very common in:

• casual conversation
• written explanations
• internal thoughts
• narrative text

Even though 少ない is an adjective, わけ is a noun-like word here, so it naturally takes だ or です:

• 〜わけだ
• 〜わけです

Japanese word order is somewhat flexible, but the original order is very natural.

The basic relationships are shown by the particles:

• 彼女は = topic
• 毎朝 = time
• 予定を = object
• 手帳に = location/target
• 書き込んでいる = verb

Because the particles show the roles, some reordering is possible, such as:

• 彼女は手帳に毎朝予定を書き込んでいる。

This is still understandable, but the original:

• 彼女は毎朝予定を手帳に書き込んでいる。 sounds smoother and more standard for many learners to model.

So yes, some variation is possible, but the given word order is a very good, natural one to learn from.