The "Riverdale" actress, 23, came out as bisexual in June, announcing that her friends have known about her sexual preferences for years, but she had not gone public for fear she looked to be faking it to get attention as her major relationships had been with men.
However, she hopes the creation of the bisexual Luz Noceda in "The Owl House" will promote understanding from others.
"I've been met with comments of 'you'll grow out of it' but I know that's not true," she tells the BBC, before adding, "I think it's important to make it more normal, as I feel in cinema and TV, the characters are usually gay or straight, there's not a lot of bisexual characters - but it should be normalised."
"There are a lot of bisexual people, including me. Before, I felt that people were going to invalidate what I was saying by telling me I was going through a phase."
Reinhart plays Grace in the new Amazon film "Chemical Hearts", a teenage girl who dresses in androgynous clothing and walks with a cane.
She says she hopes that young people now have the resources to embrace their sexuality and identity in a way kids didn't feel able to when she was a young teen.
"Times are changing, and at school, there was one gay kid who was out and comfortable with it, but some people were hiding their sexuality because they were afraid to come out."
"I hope people know they have outlets and communities who are now so willing to support young people facing decisions about this. There's a lot of open arms out there."
"Chemical Hearts" debuts on Amazon on Friday (21Aug20).