I found a cat, how do I make my current cat get along with her?

oh goodness. i had the same problem (but i am very sad one of your cats are de-clawed cuz that makes it harder for them to walk cuz it takes part of the bone and nerve and all and i would never do that to a cat but its ok, im not trying to make you feel bad) i had the exact same problem with me getting a new cat. its been 2 years and 2 days and they still try to kill each other. try putting one in a cage and putting the other ca in the room and let them get use to the cat, then put that cat in the cage and the other out, this method i heard works very well most of the time. do this frequently and they will get use to each others presence. then you can try having two people (you and another) and each hold a cat to the point where they cant scratch each other and all (like, hold their paws and all. then put them close together, also do this frequently. hey might hiss and growl at the beginning they will most likely progress. i wish you the best of luck!