popa is right. Give your child ensure or pedia-sure to gain weight. Fried foods is never a good idea. She should still eat healthy. You can also offer her an extra large portion or a second helping. Another idea is to give her more meals but smaller portions. So give her snacks that are healthy but will help her so you can give her an extra sandwich for a snack. The bread alone, even whole wheat bread, or a small bagel or soft pretzel adds calories to her diet.
Speak to a good nutritionist who can help you add healthy snacks to her diet plan so she can gain needed pounds and have proper energy. But if she gains weight from unhealthy foods she will gain fat that might have a lasting result you are not looking for in the future.