We need more roles filled like how they filled Ripley's role in Alien:
Write a unisex role. If a love interest is necessary, make that love interest unisex as well. Fill the role with the best actor for the part (best pairing if a love interest is necessary), and that's it. Don't write a strong female for the purpose of having a strong female, because that character will likely suck.
Supergirl doesn't suck.