My 3 year old chihuaha recently started snapping ?

My 3 year old chihuahua has recently started snapping at people. She has snapped at my nieces and mom when they tried to pick her up. Although she only snaps at me when I try to move her when she is asleep. Other wise she doesn't really snap at me unless she get a hold of a bone. She gets along great with my other 2 dogs (1/2 beagle& 1/2 bet hound and 1/2 weenie& 1/2 chihuahua) and cat. She's never been snappy with anyone she knows before now. Help should I be worried