When it comes to comic book TV shows, nothing is out of reach in some cases. Characters are touchy depending on the setting, but now, with the success of Arrow and Flash, virtually anything is on the table.
In the most recent Supergirl episode, titled “Red Faced”, Supergirl unleashed her heat vision to an incredible degree upon enemy Red Tornado. To the extent that later on, her powers were gone. This is apparently the “Supergirl version” of the Super Flare ability that Superman recently got in the comics. That is what producer Andrew Kriesberg told ComicBook.com:
“it’s something that actually, it’s, sort of, new from the comics. It was a Geoff Johns idea, which was that Superman’s — or any Kryptonian‘s — cells are, basically, suffused with solar radiation and that’s where they get their powers from and the heat vision is an expulsion of that energy,” Kreisberg had said. “You could actually just, basically, run out and you would need to recharge. I was such a fan of that comic and that run and talked to Geoff and said, ‘Could we do something with that?’ and he was like, ‘Absolutely!'”
Now in the comics, the Super Flare turned Superman into a bomb of sorts, and his solar energy went everywhere, destroying much of the surrounding areas. For Supergirl, that didn’t happen. It is known, and accepted, that Heat Vision does deplete Superman’s and Supergirl’s powers much quicker than their other abilities, especially when they amp it up. That could be seen as what’s happening here. But the Super Flare? That’s up for debate.