What did she pay for it? if the older technology was significantly cheaper than the newest greatest, snobbiest product then buying last year's model was the smart move.
The difference between 780 and 1080p is nominal and only an issue with blueray right now. Plasma looks better than LCD in my opinion and the field of vision is a little better.
Maybe she got a great deal. Maybe she likes the way the plasma looks. Maybe having the latest and greatest isn't an issue with her. Maybe she's not a tard at all, maybe she's smarter than you give her credit for. Maybe there's a reason she didn't listen to you.
BTW I have a samsung 52" plasma tv and I love it. Yes it has 1080p but I have never watched anything in 1080p on it
afaik. If I have I didn't notice any difference.