Every Supergirl ranked from weakest to strongest
Honorable mention: "Kara" / Lindsay Harrison from Smallville
Before we dive into the rankings of all our live-action Girls of Steel, we have to acknowledge the Supergirl that never was. An odd sentence I know, but when Adrianne Palicki showed up in the season 3 finale of Smallville calling herself Kara from Krypton, you can bet that more than a few DC Comics fans raised an eyebrow and questioned, well, everything.
It ultimately turned out that this wasn't actually Clark's cousin or the future Supergirl, but a woman named Lindsay Harrison who had been missing since the 1989 meteor shower that Jor-El was using to convince Clark to embrace his destiny. That didn't change the fact that she possessed all of the superpowers that Supergirl is known for, including unbelievable strength, speed, hearing and the ability to fly. Oh, yeah and she was stronger than Clark.
She also had the unexpected ability of unleashing energy from her hands capable of disintegrating anything in her path - a power Kryptonians aren't known to possess.
It's unclear if this was the real Lindsay Harrison or just a lookalike created by Jor-El to get Clark to live up to his destiny, but she wasn't Supergirl, even if she would have been an incredibly formidable one.