Thanks for your question. I will try to help.
You also have to try and show them that she has continuing obligations in her home country which will continue after the visit and therefore convince them that she is not a risk of overstay because she at present has compelling family and social/work ties to her home country which mean that she will not attempt to secure a permanent stay here whilst she is visiting.
This means that you have to submit things like a letter from her employer stating she has a job (if she does) and is expected to return to continue that job, return flight tickets, evidence of continuing accommodation (eg. tenancy agreement of evidence of ownership of a property), bank statements showing the money she has available, letters from relatives/friends confirming any obligations she has to them.
The key is showing that she has other commitments in her home country that, although she can take a short break from to have the visit, she will be compelled to return home because these commitments demand her to return home.
The most important thing is evidencing her continuing employment, assets (eg house) that she has in her home country and family relationships (eg husband, children, parents that she looks after etc)
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