K's mom-

It could be allergies,
or it could be one of these: http://www.animalhealthchannel.com/felinechlamydiosis/ http://www.animalhealthchannel.com/rhinotracheitis/ http://www.animalhealthchannel.com/calicivirus/
Your best bet, if it lasts for more than a few days, is to seek advice from your vet. I hope she feels better soon, and good luck!