Complex sentence: Like Oliver, Isabel was also trained by Slade in martial arts, but she later injected with the same Mirakuru drug that was given to the latter, augmenting her physical and mental performances at no cost as Isabel is already insane.
Split into simpler sentences: Like Oliver, Isabel was also trained by Slade in martial arts, but she was later injected with the same Mirakuru drug that was given to Slade. It augments her physical and mental performances at no cost as Isabel is already insane.