Q: Letting Skitters outside?

anymore Skitters alot of the time will only go outside if I let her out and this is a major problem she is my dog but I have stuff I have to leave the house to do and she can't always go with me. My sister invted me to go to seaside with her but Shorty is sick so I can't go anways if I could have gone I would still of had to say no because of Skitters new behavior she will go outside for me but I don't have to go outside with her. But she won't go outside for anyone else at all so I can't leave her to suffer. Does anyone know why Skitters is doing this?