Mad obsession huh ? Please note the way AIs operate - if they have been programmed with a goal they may continue to peruse it at cost of everything else, even at cost of their own existence, depending on how the AI is coded.
Grace might have calculated that the new stage in evolution is worth any cost, or at least a planet worth of whatever. The key here is not what she is willing to sacrifice, but what her goal is. Her goal could to benefit herself or to advance the human species to the next stage of consciousness. If it's the former then it's just bad writing - why would she want the job of controlling billions of what amounts to idiots to her? if she want another job she could just work as the local vending machine instead. If her goal is the later, she's fundamentally benevolent, however applicable that word is to a artificial being.
As for killing everyone - that's just bad writing. As we have probably concluded by now, if she tried thing the sensible way, it'd not be any fun.
Tentacles? I am sure grace have plenty of tentacle-less clones. I do hope grace get her next job as a sentient capital ship. Every Sci-fi world need one of those.