She'll find a way to warn Charlie to be careful without giving him the details. Forewarned is still forearmed.

She watches Sherlock's hand work on his arm for a moment as she thinks. Of her current available options, accepting Sherlock's warning as genuine for the time being and proceeding accordingly seems best; finding out just how this entity operates is important if it's real, and won't do any actual harm if it isn't.

"Is it just the dead that it looks like?" asks finally.