Leash-trained cat is driving me crazy!?

I am a veterinary student and live in an apartment with my one year old white cat, Margie. I have taught her to walk on a leash and she does very well and loves to go on her walks every night. There is only one problem: when she is in the apartment she sits at the door and meows and yowls constantly to go on a walk. It is becoming difficult to study with her constantly meowing. I go home to our farm every weekend and she is outside most of the time then doing whatever barn cats do. I understand why she meows, and that letting her outside all weekend and walking her on a leash every night only reinforces her love of the outdoors and the meowing to go outside. What I want to know is if there are any behavior modification techniques I can try to at least decrease the meowing. It is getting to the point I am considering leaving her on the farm full time, but I love her to death and don't want to do that. I have tried her with water, and it does help, but I don't want her to become fearful and I can't be walking around with a water bottle in my hand all the time! Any help would be greatly appreciated and if I am forgetting any details please ask more questions. Thanks!