Learn Hardcore Japanese: haha ha totemo tyuuibukai hito desu.

は is the topic marker. It tells us that 母 (“mother”) is what we’re talking about. In English you might think of it as “As for my mother…” or simply “My mother…”

Why isn’t 私の used before 母 to mean “my mother”?

In Japanese you often omit possessives like 私の when context makes it clear who you’re talking about. If you’ve already said “my mother” or it’s obvious from the conversation, you can just say 母.

What role does とても play here?

とても is an adverb meaning “very.” It modifies the adjective 注意深い, intensifying it: “very careful.” You can’t use とても to modify nouns directly—only verbs, adjectives, and other adverbs.

Is 注意深い an い-adjective or a な-adjective?

It’s an い-adjective, despite being a compound of the noun 注意 and the adjective 深い. Because it ends in い, you treat it like any other い-adjective: no な is needed before 人.

Why is there no な between 注意深い and 人?

Since 注意深い is an い-adjective, you attach it directly to a noun. If it were a な-adjective (like 静か), you would say 静かな人, but for い-adjectives you just say 注意深い人.

What exactly does 人 add to the sentence?

人 means “person.” Adding it turns 注意深い (“careful”) into “a careful person.” Without 人, you’d just be saying “(she) is very careful.”

Why do we need です at the end?

です is the polite copula, basically the polite form of “is/am/are.” It makes the sentence appropriate for most everyday situations where you’re not extremely casual.

Could we drop 人 and still make sense?

Yes. If you say 母はとても注意深いです, it means “My mother is very careful.” You just lose the explicit “person.” Both are natural; adding 人 emphasizes “a careful person.”

Can we use が instead of は, like 母がとても注意深い人です?

You could, but it shifts the focus. 母が…です often answers a “who?” question (“Who is very careful?”). 母は…です states a fact about your mother. Use は to introduce the topic and が to identify or emphasize the subject.