Husband is thai and wife is indian . due to pregnancy and delivery done in india due to some complications could not come back before the yearly visa  renewal.now the wife plans to return back after recovery and there is gap of 6months or more from last visa. How can one apply back for visa . Do one have follow again as same for first time visa .

or showing medical documents would help ?

Since her extension has now expired she will have to start all over again and will need a visa to enter the country. Having medical documents would not help.

She will need a new non-o visa based upon marriage and then apply for a new extension of stay (it is not a visa).

If possible she should get a single entry non-o visa before returning.