Shadow Lady
She is pretty good. She can equal Chun-Li but Chun-Li still has the "Air Raging Demon" to make her a bit better. Which you choose is your choice. Better yet, team them up to be a challenge to anyone.
Special Attacks
Drill - QCF+P
Electric Burst - DPM+P
Seeker Missiles - QCF+K
Lightning Kick - K rapidly
Neck Braker - DF+FK
Axe Kick - HCB+K
Super Attacks
Big Bang Laser - QCF+2P
Galaxy Missile - QCF+2K
Final Mission - [B],F,B,F+3K (Level 3)
Combos
D+WK, FK, U+WP, WK, MP, MK, FK rapidly
This is basic air combo that leads into the Lightning Kick. Just keep on hitting the FK button to deal more damage. Try to catch them while their on the ground with the Lightning Kick also. That should deal some good chip or regular damage.
D+WK, FK, U+WP, DF+WK, DF+MP, DF+MP, (DF+WP, DF+WK, DF+MP, DF+MK)
This is an infinite that works well. Just hit them with a hit then launch. From there, follow up with a WP. Then hold DF and hit WK, MP, and MK. The MK will be a head stomp which will allow you to continue with the next 4 hits. After you fly up off the screen, it becomes a matter of timing. If you can catch them as soon as the match starts, it could be a good minute or so before you and the carcass drops when they die.