My wife tends not to get much direct sunlight, and she has low vitamin D.  I just ordered fish oil and I’m wondering, will that help with her vitamin D (I had heard that some fish oil is a good source of vitamin D)?
Fish-oil doesn’t contain enough Vit D. The liver oils contain more, but in case of deficiency you need to supplement specifically with Vit D. Get a physician to test it and find the exact level of deficiency so they can prescribe an appropriate amount to supplement.