My chihuahua won't eat?

I have a 10 month old chihuahua & today she just hasn't been eating. I've been encouraging her nonstop all day. I've even placing her in front of her bowl & the most she's done is stick her nose inside the bowl for a few seconds, pop a piece of food in her mouth, & then puts it back & walks away. Her stomach's been grumbling nonstop but she just won't eat! What can I do to make her eat?