It's 2x50 pounds. In addition to the footnote, they have a box at the top of the page
Unfortunately web design isn't always the easiest thing. Looking at the layout of this page and the baggage allowance table, there is no way to add an additional column showing two 50# bag symbols without either shrinking the other columns a disproportionate amount or widening the table, which would then throw it out of alignment with the remainder of the page. Perhaps they could get rid of the 70# symbols all together and just show two bags and have a separate table to show the weight restrictions. It could be this is a temporary fix until they have the time/resources to more fully redesign the page in the future. However I think their current method is sufficient having a box before you even encounter saying 50lbs per bag and having the footnote clarify that the 70# symbol isn't meant to represent the weight restriction for premium select.

Also, regarding first class vs. premium select weight/bag allowance. Unless your wife is on a split fare, her fare is a premium select that has the domestic segment in an available first class seat (there are accounts of a premium select seated in domestic Y when first class seats aren't available), but the underlying fare is still premium select. So, no she doesn't get 70# going over, she gets 50# because that is the allowance for the premium select fare she is flying on.