Megaman 10 confirmed

[Ton]

intro to super metroid, super metroids ending;
baby metroid in metroid II
adam and federation in fusion
space pirates, chozo in zero mission

Does she? Or is that what you're projecting onto her?

those are what the games say and official canon recognizes that~

but backstory is not characterization. Characterization is how they react because to their backstory. Why is that backstory important

her parents were killed by the space pirates, and the space pirates also hold a hand in the destruction of the chozo iirc; it also explains her suit and upgrades, which are chozo relics~

being a bounty hunter offers the kind of freedom necessary to pursue that

her motivation is pretty obvious bro

Maybe she cared about that Metroid at the end of Super Metroid, or maybe she just saw it as a lucky break and immediately moved on.

Evidently she cared enough to keep it alive.

You're speculating an awful lot. There's nothing solid in-game to say why she makes the decisions she's made. Being a bounty hunter gives her freedom. Ok, but not having a job would give her even more freedom.
It's probably more like this; she doesn't know where the Space Pirates will be at any given time. She has access to the weaponry, but not the locale. That's what the Federation provides her. In return she kills the pirates and keeps the Galaxy safe. Good speculation, but still speculation. We don't know if it's true. If Samus just said that it would be canon and it would add to her character.

Similarly we don't know why she kept the Metroid alive. Maybe she felt sorry for it because it was the remaining specimen like she was and took pity on it. Or maybe she saw the opportunity to use something of immense power that the space pirates no longer had against them and the Metroid misinterpreted her willingness to keep it alive as a biological weapon as nurturing, so it latched on to her as a mother.

Both are possible and both are pretty cool. Hell, maybe it's a little of both. But we don't know because Samus never says it. She has the potential to be the most interesting of all the Nintendo characters. I'd argue that she is. She doesn't have much to contend with. But she's still plagued by fan projection and very little actual characterization.