>>i was thinking either the sweater is too hot for her and it makes her lazy. or when she doesn't have her sweater on, she is very active just to stay warm?
It could be that she feels restricted by it. Our Pharaoh Hound has a couple of coats that she does not like very well. We use them only for specific weather conditions and she seems to not mind them as much then.
My parents boy Poncho hates to wear a collar, I think he's about 9 yrs old now and he's always been this way. He is fine if he has a halter on but if you put a collar on him he slinks off to his crate to hide in his den. They save the collar and put it on him if he gets out of control barking. It's quite a neat trick really. 
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tabitha
Kayo, Kahla, and Dante'