Hi Rafi,
Yes you don't have to wait for 3 months before you could bring your wife back in a visit visa, however you would have to through the same process as you did the first time. The return visa is applicable if one has to leave the country due to some emergency when he or she is on a visit visa provided they would return to Qatar before the validity of the visit visa. Here in this case that does not apply for your wife since she is about to exhaust her visa duration.