Will I end up the same size as my mom?

I am around 15yrs old and very active. I currently am on the basketball team and i just finished w/ tennis season and i have been playing both everyyear since i was 7. I also am in strength and conditioning in school. I am very fit. I told my mom that I always wanted to stay in good shape and that i never wanted to be over a size 12. Well she says that its in my familys history and that if i am less then a 10 i will be in the hospital. Im not sure i agree with this because im the first person in my family to actually be involved in sports. What do you think?