I have a colleague in the same boat. Even though Shariah law should support your plan (assuming she's widowed and as you said, there are no other children), the state will likely ask if she has any brothers, nephews, or anyone else who can look after her.

It is possible however to bring her in on a visitor's visa, extend that visa to the maximum, then fly her to Dubai or Bahrain for a weekend and bring her back on a fresh visa.