Translation:She is taking a shower now.
She is having a shower should be accepted as it is valid in British English.
The second 在 (zai) is the marker of the progressive tense. 我吃 = I eat. 我 + (正)在 + 吃 = I'm eating. 我 + 现在 + 在 + 吃 = I'm eating now.
"She is taking a shower" should also be accepted, as the context clearly implies that she is taking it now. Semantically the word now is unnecessary