Elly's Transformation

Charlotte nodded, "Yes, right now, we are merged at one percent. I use the rest of my power to stop the assimilation progress. If I open it, the merging will continue. 

When it reaches more than forty percent, that means we will never be able to split again. Also, during that process, not only will you see a glimpse of my memory, but I will also see yours."

Victor put some thought into it, then asked, "Why offer me this then? Why not try to take my body for yourself?" 

Even in his inner world, Charlotte has control over it; Victor thinks it should be possible for her to take his body.

"I am not a monster like them! I will not hurt the innocent!" Charlotte replied with a stern tone.

There is another reason, but she doesn't talk it out because she doesn't want Victor to know. She has seen more of Victor's memory, not just a glimpse of what he thought. 

This allows her to decide that Victor is her best chance to recover.