Amanda's repped by David A. Esquibias, and he tells us ... Amanda's move to pull the plug on her conservatorship is years in the making, starting long before the #FreeBritney movement grew vocal last year.

He says Amanda filing the legal docs a few months after Britney successfully ended her own conservatorship is purely coincidental, and adds she's never even mentioned Britney's battle.

Amanda's lawyer says her conservatorship was never meant to be in place for her entire life -- the goal was always for it to end -- and within the last 2 years, Amanda and her parents realized the significant progress she'd made in coping with bipolar disorder.

Amanda was placed under the conservatorship in 2013 following a string of bizarre episodes. She was temporarily committed to a psychiatric facility and once released, her parents started taking care of her.

We're told Amanda's gained important structure and support in her life through attending AA, and has been sober for 3 or 4 years.

She's also doing really well in classes -- almost straight A's -- at the Fashion Institute of Design & Merchandising as she works toward a Bachelor's degree. We're told she's focused on using fashion as a creative outlet, and also wants to develop fragrances.

Interestingly, she's not mentioned anything about getting back into acting.

Amanda's lawyer says she's been working hard with her parents to reach the common goal of ending the conservatorship, and she's put in a lot of work and effort to get there.

As we've reported, this is significantly different from Britney. Sources directly connected to her conservatorship told TMZ ... they thought it would be in place for her lifetime, because they believed she couldn't safely care for herself and others.