I never have been drawn to DC. When I was very young I had access to a huge collection of comics that my uncles had as boys all heaped together in a big box. They were mostly silver age DC titles, some random comics, and just a few Marvel items from the late 60s and very early 70s. Even then I could tell I preferred the Marvel stories and characters.
The collection ended just a few years before Power Girl showed up in DC so I never was aware of her as a character until very recently, like well into the 2000s. I still do not like the character and I find her personality annoying and not very interesting. Also, yet another Superman-like character just does nothing for me, as I had been exposed to all those alternate versions in that box of comics.
I did some digging and could not find any third party confirmation about the drawing Power Girl progressively bigger, either in a single comic or over multiple comics. The only sources all appear to copy the story from each other and none of them are dated prior to the New 52 "reset" (which I had to look up too) on or around 2011.
Also, 2013 appears to be the start of the biggest emphasis of Power Girls chest both in the comics and out in the fan-base. Something appears to have happened that year that got everyone stirred up and parody and direct comments about her frontage became commonplace. As there is a delay between the drawing and printing of the comics, something was going on at DC in 2012 regarding what was going to be done with her and the emphasis on the bust must have been a topic even then.
I did locate the fan base determined largest depiction of her in-comic, that is not a fan generated image, and it hits right at that 2013 date. I will say that she is large, like bigger than her head big in the cover art. This particular comic has been noted as having not only the largest depiction on the cover, but also within the pages of the comic, something that issues with slightly more busty covers do not continue.