Thanks for your question.
They where they consider there is a risk of an overstay. You are going to have to convince them that there is no risk with a further application.
You have to try and show them that she has continuing obligations in Dubai which will continue after the visit and therefore convince them that she is not a risk of overstay. Things like evidence of return flight tickets, evidence of continuing accommodation (eg. tenancy agreement of evidence of ownership of a property).
You will also both have to execute declarations stating state the terms of his visit, that you are to return at the end of it, that you are both aware that she should leave at the end of the visit because it would harm the chances of any future application made to secure leave to remain in the future on the basis of that relationship and you would not wish to prejudice that possibility.
You can also submit letters from persons that know her, for example you might ask the children's school for a letter stating that your wife has seen them to ensure that they enrolled the term after the visit.
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