Lois’s answer to “I just listened to Masquerade again and it got me thinking about demons and dolphins. Do you think …” > Likes and Comments

It of course remains an open question how much of the demon's... er, spiritual essence remained after it went into the fox (in Penric's Fox.) Clearly enough to remember people it knew before, and enough to care for the fox and her kits.
Possibly enough to work magic on her own -- we saw Des independently take action in Demon Daughter, when Pen wasn't paying attention, so the living entity (human or fox) doesn't need to necessarily have volition about it.

Des does have blanket permission from Pen to act on her own in emergencies, as her reflexes and perceptions are faster, but that's more a measure of the established trust between the pair than the demon ascending in spurts. Granted it would look alarmingly the same from the outside.

With the fox, it would be more the (already humanized and trained) demon ascending in spurts, giving way as needed to the fox to attend her fox business. Dangerous but not malicious.

Ta, L.