need to shed my post accident weight gain

Hey there all you wonderful people!

i am a 31 year old girl from india, well to begin with i may sound totally retarded when i say this but never needed to think about fitness as have been blessed all these years with good health and fit body, but alas! nothing lasts forever and i had a horrible bike crash which forced me to bed for 4 months still recovering from it however 4 months of strong medication, mothers care and love gave me a weight gain of 12 kgs .phufffffff!!!!!!....now the challenege is to keep weight off and loose it as my leg cant bear my weight and have been told to loose it asap before my next surgery which is scheduled in last week of sep. i can barely walk so exercising is not an option for me. i would need your guidance and support. to begin with if you guys could share your weight loss recipies and secrets that will be awesome. also can i follow the diet calorie calculations that this site provides i mean is it accurate ...coz when i fed my todays food intake it said on the same diet i cd loose like 19 kgs in 5 weeks which looks impossible to me ...

looking forward to your support and guidance
love and Gratitude
Rashi