Evgenikós wished to converse with Velma but it seemed almost impossible under the doctors constant scrutiny of Velma and then the other creatures who had not see her. She knew some of them could converse and they might let the doctor know of her presence if she did not set them free.
She knew they were going to try to blackmail her and her powers were not strong enough for her to converse with another without speaking out loud or (converse through the mind). It would be strange if they heard a voice without a body and saw Velma talking to a person. So the only way was to talk to her in a physical presence but if the doctor found out, she was doomed.
It was not like he could trap her in a glass box— her magic was too powerful for that but he might report her to the authorities for not being human and there was only so far her magic could take her.
What she needed to do was to make the doctor trust her enough to let her in on his secrets.