She is most likely thinking how she hates waking up early and going to school. I always try to think back on when I was a kid and what were my stresses.

1. Waking up super early
2. Keeping up with school work
3. Other kids and fitting in

etc ...

She most likely had a tough morning or even week and was thinking back on the last time she got to stay home sick and how you were home.

I know it's easier said than done, but just try to see it from her eyes. She doesn't know what depression is or having a mental illness. So to her, if you're not running a fever you're probably ok enough to enjoy your day off at home.