Have I purchased the wrong bike?

[betoney]

First get her on the bike and see how she feels. Do 50 miles, than 100. If she is all "hells yes" the weight shouldn't be much of an issue, but I really think your issue will be more of "this is exhausting". 
 
I agree with this approach 100%.   I tried this a few years ago when I thought riding with the girlfriend was a sure thing.  Turns out after a relatively short ride, the hips and knee bend angle wasn't comfortable and I got the "Can we go home now?"   Now, I only ride solo.