I thought the same thing with Er Shun, but her doors to go outside have been close during my last couple visits. She can't go outside, even if she wanted to.
As for the Warthogs, during my last walk through in the pavilion, the Warthogs were on display, with access to the off exhibit area. And I'm pretty sure only 1 Warthog was present. The River Hogs were a no show.
Odds are you are just catching Er Shun indoors. But maybe she is a big suck and just doesn't like the cold.
I think it would have been a good idea to take the hogs off display for the winter and put Lucy and the piglets in there. Why have babies when no one can see them until spring? Its one thing if no one is around to see them but its another if they are off display the whole time.
I'm not so sure about Er Shun. When she has access outdoors, there's usually food put out for her. Nowadays, the outdoor exhibit is completely empty. Plus, the doors are closed. When Da Mao is outdoors on cold days, they give him the option of going indoors, by having the door open.
During my visit today, the River Hog are on exhibit indoors, and the Warthogs are off exhibit.