State residency for tax purposes is determined by state laws. It is not a matter of "pick and choose."
Has your fiancee been living in Georgia with you? If so, be aware that she may have to file a GA tax return if she earned money in Georgia or if she lived in Georgia long enough to be considered a Georgia resident. Here is GA's law on residency:
(10)
(A) "Resident" means:
(i) Every individual who is a legal resident of this state on income tax day;
(ii) Every individual who, though not necessarily a legal resident of this state, nevertheless resides within this state on a more or less regular or permanent basis and not on the temporary or transitory basis of a visitor or sojourner and who so resides within this state on income tax day; and
(iii) Every individual who on income tax day has been residing within this state for 183 days or part-days or longer, in the aggregate, of the immediately preceding 365 day period.
If she is not considered a Georgia resident, she would still have to file a non-resident GA tax return if she earned money by working in Georgia.
If her main, primary home is in Indiana, but she also meets GA's definition of Resident, then she would be in a situation of dual residency and would have to file as a resident in both states.
Since you are not married and thus cannot file a joint return, she should use her own mailing address on her tax return. Note that the mailing address on a tax return should be the address you want the taxing authority to use if they have to send you a letter or a paper check.
If your military SLR (State of Legal Residence) is Indiana, then your military pay is exempt from Georgia taxation.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
