Is it necessary to get a kitchen fire extinguisher if I have an ABC rated one already?
An ABC extinguisher should be safe for all three classes of fire. It may not be be the most effective possible choice, or the easiest to clean up after. Depending on what you think the hazards are, how willing you are to fight them, what experience you have, how badly you panic (as opposed to, for example, smothering the fire with a pot lid), and how much cleanup is going to aggravate you, a more specialized extinguisher may be a cheap and effective investment. 

Anything that reduces hesitation, or time fetching the extinguisher, is a good thing.