This is a tribute to the Legion of Superheroes movie. Solomon Grundy is powerful but lets keep it 100%. He stands absolutely no chance against a serious Supergirl. She’s on a completely different level in both speed and power. Grundy may have the durability to take hits for a while but he has no way to catch her. She would definitely be coming out on top here and showing why the Kryptonians are not to be underestimated. Supergirl wins.