Originally Posted by
Terra Firmish
My question is, when her US passport is returned from processing, would she be able to travel to the UK using the US passport and the default permission to stay for six months without any further visa, or would she need to wait until the visa was awarded and the intended date of travel came?
The later. Spousal visa is a form of family visa for leave to remain. Home Office can in fact deny entry because she has intention to stay. The trip is basically asking for troubles.
Originally Posted by
Terra Firmish
She also has a Brazilian passport, and that too would normally allow her to stay for six months. Would travelling on that make any difference?
Once she starts the application process, her information will be in the Home Office's system. Using another identity does no good (as name, gender, and birthdate are usually the matching criteria).