I give you some tips from a recent experience: basically, talking about normal tourist visa, they need to be sure that she will come back to Thailand. Based on this, a plus will be if she has a job in Thailand or own a company or any other assets. She needs to prepare a brief about her job, what she does, and a genuine tourist plan where she explain what she wanna visit and why. There are various fb groups for thai people where they post experiences every day, can be very useful for her to join them.
Yes, reading that looks like being Brunei citizen is a requirement to get the access to services, it just sounds a little bit weird to me, but maybe it's common in such little countries
Did you get some info about, or maybe, have you been there already? I was planning to do a visa run there, some people from brunei who are working in thailand say would be ok for foreigners to get a thai visa in Brunei but I cannot be sure.