It may be a no brainer, or at least it may seem like it once you realize how she does it and why.

She consumes the yellow blood cells. I realized this when driving home and thinking about it. How Hiro had the "polar opposite affect" of the others, which was a major increase in yellow cells.

I believe she does it for the same reason the garden kids are injected with yellow blood cells, it enhances their aptitude. It empowers her momentarily and she is then able to stampede and fight on.

Obviously I don't know much other about yellow blood cells, because they are made up in this universe, but I have speculation that the side effects of low yellow blood cells is profuse bleeding and of course, death. Which was what killed the first Stamin and almost killed Mitsuru.