Learn Hardcore Hausa: Tana aiki a masana'antu.

Tana is the 3rd person feminine singular form used for a present/continuous action. In simple terms, it tells you the subject is she and that the action is current or ongoing. So tana aiki means something like she is working or, depending on context, she works.

Why isn’t ita used for she?

Because tana already includes the subject idea she. Hausa often uses these shorter subject forms inside the verb phrase instead of an independent pronoun.

You can use ita for emphasis or contrast, for example: Ita tana aiki = She is working.

Without emphasis, Tana aiki is perfectly normal.

Is aiki a noun or a verb?

Strictly speaking, aiki is a noun / verbal noun meaning work or working. But in Hausa, verbal nouns are very often used in the predicate, so they function much like English verbs in sentences like this.

So even though English expects a clear verb like work, Hausa can say: tana aiki
literally something like she is in working / she is doing work, but naturally understood as she is working.

Why is there no separate word for is?