I have mixed feelings on this, too.
As I've mentioned previously, Supergirl is my favorite comic book heroine. And by Supergirl, I'm referring to the traditional blonde, blue-eyed Kara Zor-El, cousin of Superman. My first proper introduction to the character came from Michael Turner's Supergirl, so that's the version of the character that I know and love.
This image in particular captures not only the look of the character but the spirit that I believe the character should embody, and it is one of my favorite pictures of Supergirl.
So, with Sasha's Supergirl looking so different, that's why I would rather she be an entirely different character, with a different name, like Lara Kent. That way, if this new version of Supergirl proves to be popular, she won't replace the traditional Kara Supergirl in the comics and other media. But Flashpoint Lara version could exist alongside Kara Zor-El as her own character with her own comic line, merchandise, etc.
The last thing I want is for DC to gradually replace any trace of the traditional blonde, blue-eyed Kara Zor-El that I know and love with this new version due to popularity or to appeal to a certain region or demographic. Because then I would come to resent this new Flashpoint Supergirl, no matter how cool or popular she becomes.