I would like to bring my niece into Dubai from Namibia to be my children’s Nanny, can you tell me if this is possible?

Unfortunately it is not as Namibia does not belong to one of the countries from where UAE residents are allowed to hire a housemaid. These countries are as follows:
India
Sri Lanka
Ethiopia
Philippines.‎
Therefore, this request would be subject to approval by the Immigration department.

Furthermore, in cases where the housemaid and the sponsor/spouse are of the same nationality, a  No blood relation letter from the embassy or consulate is required proving that the sponsor/spouse is not a blood relative of the maid’s.