bsc1280 - My husband has suffered from despression. It made me realize that it really is a disease -- including physical symptoms -- and not just like a normal person being sad. If your wife is really depressed, she will need professional counselling and medical attention.
Pointing out practical reasons for a depressed person "not to be depressed" does not work. My husband knew he had a nice wife, kids, job, house, etc., but he still could not control his moods without help. A vacation home might help things temporarily, but not for the long-term.
If your wife has depression, it will not matter if she has a physically comfortable life. Because you are right: a SAHM with one child, a full-time helper and 1,000+ sq ft home should not be exhausted. Think of how many working moms there are with several kids!
My husband's depression caused obvious physical ailments like stomach cramps, fatigue, loss of appetite. Other people get rashes, vomiting, greater appetite, etc. So maybe a low-grade fever is not surprising.
My husband refused help at first - most depressives do. But, if your wife is serious, she will need basic tests to make sure she is not suffering from some imbalance, or anemia, or other physical problem.
She can also try the counsellors at Resource.
ReSource The Counselling Centre
The first two times, I had to physically go with my husband to convince him. But with support and treatment, he has returned to normal. Good luck to you two!