She may be on the verge of her first cold at only 3 weeks old. One of the other kids at the sitter's had a cold last week and Ollie may have brought it home to his sister.
Passing the Germs
That wouldn't be a fun experience. Come out of the womb, try to adjust to life outside of it and then be subjected to your first cold. She'll have plenty more, but I was hoping she would at least get past the first month before she got one. They'll pass them back and forth and infect their parents as well. I just hope, she is as agreeable as Ollie is when she has a cold.