If she's been a good girl all these years and suddenly is doing this and it's so out of character for her, then I'd say that a vet visit in order. It could be due to any number of things such as what was suggested in the previous post but I'd rule out illness first. If it's behavioral, there are medications that you can give her that will alter her behavior but not her personality. Please don't "get rid of her". Obviously something is wrong and she needs your help. Oh and btw, welcome to Pet Talk.