It's canon that Samus had her entire genetic structure rewritten by the Chozo at age 4. This means that puberty and multiple other stages of strong hormonal growth would likely cause havoc on her body and force drastic changes.

Adding to this, she had not just Gray Voice, but also Raven Beak contributing genetic aspects to make her a bioweapon. For those who don't know, Gray Voice was of the Thoha clan of Chozo, who had incredible combat talent, but restricted their emotions and violence. Think of them like Vulcans from Star Trek.

Meanwhile, the Mawkin, were all about conquest and strength. Samus only got the right arm and heart of the Mawkin to modify her biology and power suit to have the armcannon, but she has none of the mental blocking of her emotions and can operate at 100% power.

While her canonical looks are of the typical gorgeous woman we're familiar with, I always liked to see her be more heavily mutated, yet just as skillful as ever.