Answered on February 14,2019
This will depend on the following:
(a) If your wife is a voter for the first time then she will have to fill in Form-6 for enrolment as a new voter.
(b) In case your wife is already a voter but not in the same Assembly Constituency (such as enrolled in some other Assembly Constituency of Karnataka, or anywhere else in India), then she will need to fill in Form-6 for change of residence. (Form 6 can be used for enrollment as well for changing assembly constituency)
(c) If she is a voter in the same Assembly Constituency as you but needs only to change her address then, in such case she needs to fill in Form-8A for change of residence within the same Assembly Constituency.
(d) As proof of residence she can submit a copy of her marriage certificate or copy of the marriage invitation card.
All the forms are available here.