As far as I know, you cannot get a family visa for your sister. A family visa is only given for your husband or kids and visit visas are there for sisters, brothers, mother, father or children (some rules are different for children awell) which are valid for 3 - 6 months. In that time if she gets a job in qatar she can get a working visa sponsored by the company.

It's always the small things that make big differences.