She can't apply for a visa on arrival, you send her an invitation letter, the copy of your passport and professional visit visa, the covering letter from your company stating your position, monthly and yearly salary, then she can apply for Brunei visa at the embassy of brunei in Kl, she also need to submit the below documents together with the above documents:
her passport valid for at least 6 months
1 visa application form, fully completed and signed
1 passport style photo
marriage license
return flight ticket.