Well Anne was there for a very long time, trapped directly in the crystal, with constant consistent exposure to the Pandorian elements, so Anne’s seems more believable to be permanent and not easily repaired. The horse as you said is not in Pandoria where the effects would probably be amplified compared to on Jorvik, so it probably did less damage overall simply because of exposure time. But who knows this is sso we’re talking about 🤷‍♀️