What to do

We are known not to keep any pet for longer than a year. It just happens. We get animals and then get rid of them for one reason or another. I think we are just plagued with getting bad pets. We have had good luck so far with Bubba. He will be 1 year next week. That is the longest we have kept a dog! Now, not many people know we have a cat. She doesnt like people, she stays in the bedroom, she doesnt play with the kids. But, we have had her for 3 years...that is a long time for us. Well, for the past few months, things have been getting bad for her. She poops outside of her litter box...she throws up at your feet...and now, she gets on the table and eats food off your plate, while you are eating. When do I say enough is enough? Is it really so bad that I need to get rid of her? Will I regret it? Should I just stick it out and deal with it? I need help.