I don't have any experience riding a stiff binding, so I can't really answer your question.
It would probably depend on her athletic ability and her willingness to take risks. Is she strong? Will she pick up snowboarding easily? Will she push through difficulties? Is she interested in trying park or ground tricks?
However, a few thoughts on bindings.
The Burton Escapade is a very nice binding, but also one of the stiffest out there for women.
The Burton Lexa is not technically a beginner binding, but that's okay. It's a good binding and will be fine for a beginner to learn on. I personally think the Lexas and the Escapades are way overpriced, though, and would only buy them if they were more than 50% off.
In general, I would suggest that you stay away from the cheapest binding of any line - in my experience, they are just too hard to get in and out of, are uncomfortable, etc. If you want Union, go for the MIlan or Trilogy. If you want Ride, go for the Vxn or Dva (the RX is a men's binding). Rome also has an excellent line of women's bindings. I personally ride K2 Virtues and love them.