Hi
@messhetter74 
Welcome To BYC
You have recieved some good suggestions here.
Cleaning the wound is always good - you can use saline, sterile water, soapy water, diluted betadine, etc. Apply a triple antibiotic ointment (plain Neosporin) or Vetericyn to the wound. Blu Kote does work well, but for open wounds, it's easier to use something clear so you can monitor the wound for infection. It's great when you are wanting to hide wounds or need a quick antiseptic - I keep it hand.
Keep her separated and relatively warm (75-80F) see that she is drinking - add vitamins or electrolytes to her water for a couple of days. Once she is drinking well, then offer her normal feed with a little extra protein like egg for a treat.
Since the Leghorns ganged up on her - check her over for other wounds that may be hidden. Is she new to the flock? Any idea why they attacked her. Check her crop to make sure that it empties overnight and that she doesn't have any lice/mites.
How much coop and run space do you have (sq ft for each)? How many chickens?
Sometimes chickens will attack another if they are sick or showing weakness. If they draw blood, then they all jump in. Having enough space so they can move freely and not get on each other nerves will help as well.
What type of food/treats do you feed?
Keep us posted.