I stand to be corrected and maybe lilflyboy can confirm my thoughts.
Your fiancee can be granted the same 90 days on entering Botswana so she can most likely be with you for the duration of your job hunting should you want her to be.
Provided you do land a job and sort your work permits out she can come live by you. She will have to apply for a residence permit as a dependant on you. The rest is in the paperwork and holding your breath.
I am not sure if its required that you be married though...that will need to be confirmed. But there are a few pilots there with their girls
I must warn you though that its risky business taking the love of your life to Maun...good luck with that
The guys there act like they havent seen a decent woman in years, which they probably havent. She will get ALOT of attention.
Best of luck man