The most notable time Ace kicked ass was when a Dalek 'dissed her height, and called her small. She used an undefeatable fury to pulverate the dalek. The Doctor was probably VERY relieved once he decided Ace should travel with him, because he had been stuck with a peppy ginger banshee for two years.
After joining the Doctor, Ace went on many adventures, defeating: Daleks, Cybermen, The Master and a few more weirdos. Ace made her own explosives, and always thought it would be a good idea to throw some at enemies, which The Doctor sheepishly admitted was quite useful.
In her final proper appearance that we could catalogue, she recieved a "cheetah virus," which made her eyes go a funky yellow colour. She was ok, though. We think. She has also showed signs of possible insanity. Then again, why be grown up if you can't act childish sometimes? Meh. We don't know the answer, either.