You can able to apply the visit visa for your sister-in-law .
Requirements for applying visa for other relatives :

Copy of personal ID or passport of the spon sor.
Copy of sponsor's wife's passport with valid residence permit or residential tenancy contract.
Letter from employer of the sponsor citing profession and salary.
Valid passport copy of the visitor.
Document to prove relationship .
http://www.moi.gov.qa/site/english/departments/PassportDept/news/2011/01...