(Edited)
I assume that you are asking if your wife could change her Status of Residence from "Temporary Visitor" (which includes Tourists) to one that of a "Dependent".
The answer for that is "Yes, you can." However, since it takes about 1-3 months to process her application, she may want to apply also for a Certificate of Eligibility (CoE) when she makes the application for the change. This is because her "Temporary Visitor" Status of Residence may expire while waiting for the change to be approved.
See related post and links below.