My father was over 50 and very overweight. His father was overweight and had diabetes for the latter half of his life. The doctors told him that he’s going down the same road, so he lost over a hundred pounds in a few months. He simply stopped eating junk food altogether, limited his carb intake to two slices of bread a day, stuck to only diet drinks and stopped eating sugar and oily foods altogether, including salad dressings. He also started walking five miles every day and ten on weekends.
If a fiftysomething year old man very busy and very set in his ways can do it, so can a twentysomething year old girl.
That being said, the shadchan has some serious issues. You should demand that she ask you mechila. It’s simply assur to insult someone by calling them fat.
Going back to my original statement, you still have to work on yourself. If your weight is causing you to have trouble in shidduchim you simply have to ask yourself what’s more important, comfort food or getting married? My Mother in Law always says that there’s no excuse for a young single girl to be overweight.