My son is fourteen months old and does the same thing. I also remember my daughter going through this stage at about this age too. I think toddlers throw food when they are not particularly hungry or when they don't want to be restrained in a high chair.
When my son throws the first bit of food off his high chair tray, I say something like "No throwing food." or "No, thank you." If he does it again. I said "All done." I don't get mad or annoyed. I just remove him from the high chair.
Throwing food is the end of the meal.
I try again when I think he's hungry, or when the family sits down for the next meal.
I have also started putting a few cheerios/goldfish and a sippy cup on a small child-sized table in our kitchen. I think at this age moving around and walking is more important to a toddler than eating. My son eats a few pieces of cereal and then walks around the room and plays with stuff. I like feeding him this way better - he eats when he's hungry. Just put a three or four cheerios on the table at a time - otherwise they will get thrown everywhere. By the way, children this age are very messy. Invest in a good vacuum or get a dog :-)
I wouldn't worry about teaching manners at this age - way too Y..
Have patience - this is the age of independence. Don't get in a battle of wills with eating. Your daughter will eat when she is hungry and your house will be clean when she is in college.
T.
SAHM of three (8, 7 and 14 months)