Responses
Going by the beginning, where she had to navigate the restrictions on her actions by the setting, there's apparently things she "can't do or say" and might bring her back to the state where she was acting like a remote controlled puppet (that must've been terrifiying)
So I can't quite tell if it's a "she knows she can't tell the truth" situation or a "she tried every other angle and got too far to risk all on that one piece of information"
I just realized that the relationship between Penelope and Eclis reminds me of the relationship between the FL and her knight from Kill the Villainess except it's a bad end. The biggest difference is that the FL in Kill the Villainess admits to her knight that she isn't the person she's possessing and she needs his help so she can go back to her own world. I wonder if being trusted with that information would have changed Eclis's actions at all. Of course, there are other differences that have pretty big consequences, I'm sure. Penelope can die from anything and anyone here and the FL from Kill the Villainess could only die in one specific way, so trusting someone would be much harder for Penelope. Also, Eclis is an enslaved prince from a slaughtered nation while the knight from Kill the Villainess is a nobody orphan with no prospects, and while both are sad, Eclis's backstory is definitely more traumatizing and probably messed up his personality a good bit. Anyway, I think it's an interesting comparison between two similar circumstances.