Is weight watchers the best to loose weight?

So my mom bought a bunch of weight watchers food and now she is on a diet she lost 7 pounds in one week bye going to the gym twice a week so I want to try it and loose some weight I'm 12 years old and my weight is 151 pounds and thats alot for a 12 years old i think i want to be at least 115 like my aunt who is the same age as me