L.Y.
It is an allergy, just like eggs or peanuts, and should be treated as such. Make the school aware of it so that they include them on the allergy list. They will also need to take this into account when having snacks at school. We get a list of approved snacks to bring at my daughters school. She is also allergic to the dye and becomes very hyper and physical. Start reading the back of everything you buy! You will be surprised how many things have dye in them. Head back to the baby section, they have fruit snacks, cookies, and crackers without dye (just make sure the package doesn't have an infant on front). Juicy Juice has no dye but be careful of yogurt, some flavors do and some don't even if they are the same brand.
As for valentines day, offer to bring in the treats for the class party, that way you know they will be ok. There is plenty out there and you don't always have to go organic, or more expensive, you might just have to switch to a different brand of the same product.
I hate for my daughter to be separated or singled out and have to have something different so I would much rather provide for the whole class then have to make her have something different and wish she was having the brightly covered dye-filled treat with everyone else.
Eventually you will do it out of habit but until then, plan for extra time. Good Luck!