Graendal might like to show it all off, but she is definitely picky about her pets. She likes both beauty and power/social status. Possibly she may have some skill at Delving too, so it's reasonable to assume she'd examine a plaything before having fun with it to make sure it's safe.

Balthamel however, apparently had quite the reputation as a lecher and womanizer, and the DO amused himself by making him a woman, and I wouldn't be surprised if the "body donor" was the sort of prey Balthamel enjoyed. I think Aran'gar didn't spend as much time fooling around as Balthamel because she seems like she was on a tighter leash.