Totally normal during the 1st trimester. Let her sleep and rest whenever she wants cos her body is going through alot of hormonal changes hence the exhaustion. If she has started morning sickness, it'll be worse. But fret not, she'll start to feel a lil better in the 2nd trimester (hopefully, though not all). Do try to avoid taking panadols or self meditate w/o gynae's prescription which may or can be risky for her pregnancy. Remind her to take folic acid daily which is very important for baby.
When she reach her 3rd trimester it'll be back to exhaustion plus aches and pains everywhere. She might also suffer from insomnia. So happy to know that you care for your wife cos not every husband does. All the best with her pregnancy!