How Long Is Dosage Of Levothyroxine Required For Hypothyroidism In Child?

Hi there, I have question one of my friend have a 11 years old daughter she is recognized as hypothyroidism and started levotyroxin 5 days a week and she has used it since 3 years ago and now she is immigrant to Canada and her doctor said that she can stop using levotyroxin one year after she started to mense , is it through . Can she stop using Levotyroxin or she have to continue lifetime?
Thx,
Farzaneh