At what age is a child considered an adult in the state of Alabama?

My sister is turning 18 years old in January and planning to get married. However, our mother has objections. My sister will still be in high school so she is worried that because she is still in high school she wouldn't be considered an adult and would be under out mother's control. So does anyone have any... show more My sister is turning 18 years old in January and planning to get married. However, our mother has objections. My sister will still be in high school so she is worried that because she is still in high school she wouldn't be considered an adult and would be under out mother's control. So does anyone have any information that could help?
Update: People who do not have serious imput should waste their own time and not mine by providing stupid answers.
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