Once there's been an okay given by the vet and you're satisfied with it completely, start to look at the household.
Start with the inside, has anything changed? Whether it be a large or small change, any change that a cat doesn't like can result in the behavioural changes that you have mentioned.
Then start with the outside. Are there any cats, (neighbourhood, stray or feral), that you know of that visit your yard during the day or night? Something may have occurred that has upset your cat. Does the living room have a window to the outside world?
You may want to provide your cat with a litter tray in the living room, just in case it is a situation where she is unable to make it to her usual litter tray on time when she does have to go.
Has she just recently started to cry all night and day? Or is this characteristic for your cat?