It could be something as simple as she's just not feeling the greatest. If her body's fighting something, that can suck the life out of a little person. I wouldn't read too much into it at this point. If it goes on for a long period, then maybe something's up. But for now, it could be something as mundane as an impending bug. I think, also, that kids can get into a funk as easily as we can. I know for myself, depending on the weather or different factors, it can affect my mood and sometimes I'm just not as cheerful as I usually am. I have times when I'm more sensitive and emotional than others, and there's not really anything specific causing it. I would imagine kids go through some of the same. I'd just give her lots of hugs and cuddles and see if she doesn't just come around on her own.