Seems she dreads that back yard for whatever reason. Remember, most cats like to sleep about 12 to 18 hours a day in a nice comfortable place.
Or maybe she just wants a bit of love and attention from you. It's no fun being a cat when your whole life is just sleeping on a portch and then going out into a yard to play, and being brought in ONLY when others have a few minutes of time to play. Cats often get bored pretty fast when they are on their own.
Instead of just opening the door so she can run out to the back yard, pet her for awhile until she purrs, talk to her, play gently with her a little, and then walk out the back door with her as she chases a string or whatever. This will cause both of you to bond to one another as well.
Also, when you let her out, make sure she always has food, water, in a nice comfortable place protected from heat, cold, wet weather, wind, and direct sun if she's going to be there for some time. Or you could have some food literally "waiting" for her outside so that she can hardly wait to go to the back yard to see what goodies are in her dish. Maybe you could put a few treats in there.
To be honest though, most cats prefer to sleep in the house in the soft cozy bed of their favourite human. While some people portray cats as being aloof it's pretense for the most part. Most are independant but they really do love to be close to their favourite owners. Some cats love to be so close to them that they will literally follow them from room to room if the owners will be there for awhile.