Is it safe to use flea shampoo on a Cat's open wound?

I'd try to keep the shampoo out of the wound as much as possible -- it would definitely sting and burn. You may have better luck trying a product like Advantage, Frontline or Pet Armor. They all work well; Pet Armor is cheapest and is the generic form of Frontline. I use it, works great and is endorsed by the national humane society. I buy it at Walmart. Watch the wound for swelling, excessive redness around the edges of the wound and drainage that is yellow/green, looks like pus or smells bad. All of those indicate infection. Trimming her claws will help prevent her from injuring herself. Flea combing is also helpful. Be sure to have a cup of water with a little dish soap in it nearby so you can drown the litter boogers! If she's got a bad infestation, chances are there are flea eggs in your carpeting. There are various sprays you can buy for that. Good luck!