Y.,
My son does this on a daily bases. When it goes on for more then 12 hours I know he his getting sick. Shes probably has a sore throat and cant swollow. My son has tonsillitis for the third time in a row and he always has ear infections. Also, he is getting his 2 yr back molers. See if she will let you look in her throat, I bet its red and swollen. She may have an ear infection as well. My son never says anything so you dont know untill its a little late. Just a little grumpiness, restless sleep and not eating. He will put food in his (too much) mouth and you can tell he is hungry. Make an appt for her in the morning so you get her medican quickly.
I am taking my son to see and ENT Dr this week. He is 2 1/2 now and has been doing this from about 1 yr. Its getting old and hes in his 5th pertile for weight.
Give her lots of cold things like yogurt untill you can get her to the Dr.
Good luck,
SAHM TLee