It is doubtful that there is an easy way to install a power passenger seat in place of a manual one. I think that the "better" Pacifica seats will be leather even if manual. It might seem odd to have leather in the front and cloth in the back.
As you may have discovered, it is a good idea to consult significant others before making large purchases.
If the van passenger seat is that uncomfortable to her, maybe you can ride with her in her car. It sounds like only a limited power seat will be comfortable to her.