"She can eat whatever she wants and not gain a pound!"
So I have a rant about weight loss.. Far too often, I see people who look at others and say, "he can eat whatever he wants," or, "she eats a ton of junk and stays skinny!" For your own sanity, stop it.
The old saw, "You put this weight on over years, you can't lose it overnight," holds true here too. At a high level, ten pounds is around 35,000 calories*. Taken over the course of a year, that's just 96 calories per day. That's the difference between losing five pounds in a year and gaining five pounds in the same year. Less than a tablespoon of olive oil, each day, is the difference between maintaining weight and gaining ten pounds over the course of a year, or nearly a pound every month. 100 calories per day is a stunningly small amount, burned through just 20 minutes of walking, a half hour of cooking, or any number of normal, every day activities.
It's not that others can eat whatever they want and not gain weight. Saying that sets you up for long-term defeat. They simply regulate their diet better, and match the calories in to calories out more effectively. Once upon a time, survival was driven by being able to pack on the fat in times of plenty to survive through leaner ones. We're just better adapted to that.
Don't let that stop you from losing the weight though! You're not doomed to forever eat more than you need. You can control it, and impart upon yourself the same eating habits that others have developed, whether innately or through training themselves too. Small differences, like one tablespoon of fat every day, is the difference between success and stagnation.
* If you don't like my number, feel free to substitute your own, but don't let that disagreement detract from the central premise that small changes, made habit through consistency, are key to long-term success.