And besides, I could always clone Yumiko.
Cloning would still require me to kidnap and dissect her for her genetic materials. By me, I mean Legion because I don't want to get my hand dirty, literally speaking of course.
Legion is just really good at kidnapping and molesting a person. He had plenty of experience in another reality. He can also copy her memory and personality more or less perfectly, allowing me to truly test her power and whatever biological ability that she is hiding.
Obviously, examining her ability inside a spatial dimension is not as good as doing so in the real-world with realistic conditions unless I emulate the world and everything within it, including people.