I'm married and filing jointly. I am act. duty military and a TX resident. My wife lives and works in SC and is a CT res. Would the SC return be filed as a non resident?

It depends.

If she worked and lived in South Carolina for all of 2019, she may have to change her CT return to a nonresident return.

If none of the requirements apply as listed above, she can still file as a CT resident.

If you determine you are still a CT resident, then yes, you will file a nonresident SC return.

Under the 2018 revision of MSRRA, your wife may claim the same domicile state as your HOR/SLR state, even if she's never lived there.  Therefore, in the My Info section of TT, you may both enter TX as your State of Residence.

Her income is not subject to SC income tax as long as you are in SC in compliance with military orders, and she is in SC solely to be with you.

Also, she does not have to file in CT since she may legitimately claim TX as her home state for tax purposes.