So took you advise.. Already had the backrest.. Went this weekend and bought the wife a '15 Heritage... She has a new found respect for highway driving on two wheels. She will probably still ride with me on Justice more often than not but gives her the option, and an around town bike for me if needed... 
I bought my wife her own back in 2009 and she has not been on the back of mine for more than 100 miles since. She hates being a BSR . I think one becomes a rider or chooses not. I see very few ladies that ride %50 BSR and operator.
If and when I do have a BSR, sometimes the daughter, I can take it off if it is ok FOR US BOTH. Since the things come on and off easily it is not big deal to have one when you want and remove as desired.