What books is she studying?

What books were being studied by her?

What books are being studied by her?

What books will be studied by her?

What books should be studied by her?

All of the above

This is a sentence of Present Continuous Tense.

Present Continuous Tense

Active Voice: Subject + is/am/are + First of verb + ing + obect.

Passive Voice: Object + is being/am being/ are being + third form of verb + by + subject.