Win 7 OR Win 8

I am buying a new comp for my Mother-in-law on Friday. She is in her 80's and has an XP machine that needs to be tossed. I am on a tight budget but I want he to have something reliable. I couldn't afford to get one any sooner so on Friday, I am heading to Walmart or Best Buy. I am wondering if I should buy her a Win 7 machine or Win 8 AND, since I have not been keeping current...if Best buy is selling a computer with Win8 is it 8 or 8.1??? Is there a difference... or is 8.1 generically referred to as 8???:rolleyes:

I am looking at buying her just the tower, as I have given her a decent flat screen monitor and her mouse and keyboard are OK as well. :)

Thanks to All & Merry Christmas

Andy