There are 2 things that make this interesting. First, as mentioned before, the $177.99 includes the sales tax the $188 doesn't. What the 188 does include is the $20 advance purchase discount.
So she upgraded from a ticket that cost about $164.81 + 13.18 tax to a ticket with a gate price of $208 + $16.64 tax for a total of $10 + .80 tax. I guess the big question is what happened? Did they bridge the price of the 2 day ticket up to gate price before upgrading? Did they charge her the advance purchase price on the upgrade? But, in any case, this is not the previous paying the difference what you paid and the gate price of what you want (losing any previous discounts you might have had).
I will be curious to hear other reports before my trip in January. I have an old 1 day park hopper I'm planning on upgrading to a power pass. And if the results look promising I'll upgrade a 4 day park to park pass I purchased before the latest price increase to a Power Pass as well.