If we were get married after she came over on a fiancée visa, would she have to go back to the UK? Or could she stay and work towards a work visa or green card?
once your fiancée is in the United States and you are married you complete the process for permanent residence 'Green card' while she is in the United States. During the process she may receive work authorization.
Okay. That's a possible outcome, and probably the most likely. It seems very difficult to have someone petition for your work visa unless you work for a multi-national company that will transfer you. The land of opportunity is not so easy to get to apparently.
Thank you very much for your advice.
I agree with all these comments and add that the fiance' visa may take a bit longer than 5-7 months.