Since everything, to my knowledge, remains the same every time, perhaps you're right in saying that she just doesn't feel like playing.
It's a bit frustrating, though. I don't take her out everyday, so when I do I want her to get the exercise she otherwise can't get in her cage.
Also, I don't like when she tries to burrow between my legs or crawl up my clothes because I could accidentally hurt her with the slightest move!