She wants to make her partner out of the best materials possible.
And because she trusts her partner will answer to her good will, Rat continues researching.
Even if the body turns out to be a failure, she could merely switch it out… If she made a system like the Dragon Emperor’s core stones, she could just switch its soul between bodies.
Gaelion’s a good example.
The True Gaelion lives within the child one. If they want to switch, they can.
Though, it seems there’s a time limit for switching.
Perhaps Rat wants to make her partner an emperor.
“Well, while you’re at it, make sure to take care of my requests as well.” (Naofumi)
“… It’s not like I can defy the Marquis.” (Rat)