i have written many such instructionals as the best method to fatten a woman. there are several ways.
in these modern times, the easiest way is to feed the woman with many such processed foods as are widely available and inexpensive to the public. while this is effective, she will run into health problems much earlier than with traditional methods.
my prefferred way to fatten a woman is to feed the subject with massive amounts of high glycemic natural foods like honey and dried fruits to induce insulin resistance, and to fortify this with high caloric foods like nuts and full fat milks and creams fresh from the udder. this should be in addition to standard meals, so feed her these throughout the day every time she is not eating a full meal and encourage large and frequent meals as usual.
if she is thin she should reach the stage 1 of fatness very quickly. the later stage of fatness she is at, the longer it will take to reach the next level. think of it as leveling in an MMORPG: the early levels are fast and easy and the later levels take patience and expertise.
I recommend the traditional methods of fattening because while she may not fatten as quickly as she would with the standard modern methods, she will stay alive substantially longer, allowing you to fatten her for many years to come.
when you detect that she is about to die, and this may be the same for all of us with global nuclear destruction being at our front doorstep, you can throw all caution to the wind and just feed her, feed her, feed her more and more calorie dense foods.
i recommend doing this with cannabis and alcohol
i also recommend using products like this
https://corroshop.com/products/10506 to further accelerate the weight gain.
good luck and best wishes to you in this most worthy of duty of man