Although she is shaped like any bird in outline, Hestril is a naked hollow metal armature, all coarse with corrosion and rough with rust. Those iron bones are stripes backlit by the fires always roaring within her frame, feeding off the various poisonous gases abundant in Downwarp, the land of entropy in which she dwells, has dwelt as long as she can remember, and cannot leave. She is untouchable, burning and sensationless. She is a recluse, resembling the archetype of the hermit. She needs noone else to mate with or to speak to- although she is sought out on occasion, and on occasion she herself seeks out other places to expand her wisdom, for the quest of wisdom is what drives her on.
Her successive selves are born parthenogenetically, so if she is to be called anything she may as well be called female, though she needs no-one. At the completion of a forty-nine-hour cycle, the phoenix's chemical flames have finally damaged her body beyond repair, and she crumbles into ashes. All that is left is a blackened metallic sphere from her core, which had cooked and incubated in that fire during those hours. It is her heart, and it is her egg. It opens along narrow seams, unfolds, hinges out, constructions based on a Hoberman sphere, illuminated by a little pilot-light; and then it is Hestril's new body, an origami of two-sided ash-black and bright newborn silver. She reboots her memories. After a few moments she has absorbed enough ambient pollution to bring her fire to full strength again, and continues on as normal.
Hestril's life focuses around meditations on her beliefs as a rust-shaman. Hestril not only considers herself a self-contained family unit (she is her own mother, wife, and daughter) but she also considers herself a goddess, or a trinity of goddesses (maiden-past, woman-present, crone-future) or farther, she believes herself to be an entire self-contained pantheon which has given birth to itself innumerable times in succession. You could say that Hestril is rather full of herself- literally and figuratively. She can contemplate her self-centered religion at great length, but she does have genuine wisdom to divulge... if she decides that someone on the "outside" matters enough for her to divulge it to them. Her personality could be summed up as (ironically enough) cold. She's not at all cruel or heartless- she just finds you to be irrelevant, and it's hard to guess what she'll find to be sufficiently engaging.
She may be one of the Transcendi. Whether Hestril is actually a goddess is up for speculation (for other people in the Mess, at least- she has no question in her own mind, and does not care what other people conclude) but she does not have any unusual powers or supernatural control over her surroundings. Externally, she's just yet another bizarre civilian who has taken outlandish measures to cope with the all-crumbling Downwarp.