"Shelly" (original name lost to time) is a ghost/figment encountered in Eric(a)'s Memories. First encountered inside a "villa" located inside a flooded and ruined castle, she initially gives the impression of an enemy (not helped by the skeleton in her room, presumably her own remains), but quickly turns out to be a hospitable and charitable person intend on helping out the team... if not without some dark undertones regarding the things she says.
Personality
"Shelly" seems to have been a young woman of noble birth, as well as a researcher of arcane magic. While the time since her death has taken various memories, including her real name, she acts as a gracious host and allows Eric(a) and group to search for clues on how to proceed by studying her room's book collection and looking for useful items.
While "Shelly" appears kind and helpful, there is an undercurrent of wrongness to her. For example she cares little about the effects of earth quakes on large cities, knows about dangerous cults, and even admits to having visited many worlds, including but not limited to Thrudmadra and even Earth. She apparently also commited human experiments, but is unsure why she did any of her research beyond looking for a cure for something she does not remember.
At the end of the memories, after Eric(a) went through the true memory involving meeting Isabelle an indeterminable amount of time prior to being stranded in the camp, "Shelly" stands by Wendy in the void room, the only place that has not already crumbled into nothingness. There, she asks if she can join Eric(a) to find out more about herself, similar to Wendy, and completely submits to the latter's will as well as providing new knowledge.
Relationship
The relationship with "Shelly" is a fairly simple one: she provides a wealth of new knowledge (so much in fact that Wendy has trouble processing it all, and likely still will for a while afterward) and completely submitted herself to Wendy's will. In exchange, she only wishes to not die again, and see the world. Eric(a) agrees to this deal, but may voice concern if "Shelly" acts up.