To be honest if people think about it the glass tank she is in now probably doesn't give her any less space than that in many collectors or breeder's racks. I would say it is slightly cramped, but not obscenely so.
Secondly how big a tank!!!!! Really a 7ft long tank, by 5ft by 3 is really far too big. It's good to give them room to explore if you want but it'll cost a fortune, you would have to make it yourself and then pay a of money to heat it too-just for 1 corn snake? A tank that long is large enough for a burmese python! Maybe 3 1/2-4ft by 2ft would be better and still be perfectly spacious for a corn.