What if when a female AMP has a mane mutation, she starts growing a mane in her adolescent stage, just like the males do. If maneless males dont have a mane in their teen years, maned ladies should.

Example 1 : Mane Feathery, Mane Frizzy, Mane Noble, Mane Shaggy and Mane Succubus. All these manes add colour to the lady, so in the teen years, their extra fluff would be the mane colour.

Example 2 : Mane Fluffy, Mane Fuzzy, Mane Imperial, Mane Ruffled, Mane Scruffy, Mane Silky, Mane Villous and Mane Whiskered would all have their extra fluff stay the same colour as their base.
Even with the overgrown fur. It only shows on adult females, so why not the teens too?