Is getting a good deal on a CR80 more important than your fiance's comfort level? Maybe this bike is really for YOU and not for her, hmm?
Why not get her started on a CRF150, CRF230, or TTR125? A small-bore four stroke will be much easier to learn on, and a lot less likely to "loop out". And compared to a CR80, they are plenty "slow" to begin with. Enough power to get her through obstacles, but not enough to scare her off.
That said, if she wants a street bike, I'd steer her toward an MSF safety class.
http://www.msf-usa.org/
It might be easier on both of you if she learns how to ride from someone else (a stranger). Then, once she passes the class and is comfortable with all the controls and workings of a bike, you can introduce her to the dirt bike world. In either case, she'll be ready to take her street bike exam after the MSF class.
If you insist on getting the CR80, you can put a flywheel weight on it-- that will slow down the power output a bit, and help keep it from stalling.