I know people who use a .243 on elk every year as well and most are successful. I wouldn't recommend it for elk but if you are backing her up and that is what she is comfortable with then that is the best chance she has for success. Use at least a premium bullet like Barnes TSX, Swift Scirocco, or Nosler Partiton.
My recommendation is if you can afford it and I know it isn't what you wanted to hear. Look for a new/used rifle in 7mm-08 or .308, even a 6.5X55 or .260 would be a better choice than .243 Win for elk. Have the stock cut down to fit her properly there is time before elk season begins. Using 140 to 180 grain bullets will greatly increase your chances of a successful elk hunt.
My recommendation is if you can afford it and I know it isn't what you wanted to hear. Look for a new/used rifle in 7mm-08 or .308, even a 6.5X55 or .260 would be a better choice than .243 Win for elk. Have the stock cut down to fit her properly there is time before elk season begins. Using 140 to 180 grain bullets will greatly increase your chances of a successful elk hunt.