Any kind of yogurt without artificial sweeteners would be fine. The amount of sugar in there is really pretty minimal, especially compared to fruits and veggies. If you can get just plain yogurt, that would be ideal, but a spoonful of anything you have around would help.
Will she eat her food soaked with some water? I use that technique to get meds into my horses. Every meal they get is soaked anyway, so they don't even notice any meds they do need. Works like a charm. My ducks will eat about anything I feed them, so I've never had to deal with a picky one.
We have also been having some darned weird weather down here. Even mine are not as active as they normally are just because it's been cold and breezy. They stay huddled down more to keep warm. They just never have an opportunity to get used to the cold weather down here like they do up north, so it affects them more. My big horse has even been laying down recently, and the only time she does that during the day is if she's cold. As long as you can keep her eating some and keep her drinking, and give her some yogurt and electrolytes (the kiddie stuff would be fine), then she should be just fine.
The only animals I have that don't seem to care about the weather swings this year are the chickens. Even the cats don't like how cold, wet, and windy it has been.