i can't even begin to comprehend how you could deem this "too harsh".
throwing a tantrum at breakfast = not having time to eat. period. makes sense to me.
she is lucky that daycare offers breakfast, to be frank.
look, my job supports my family, which is my #1 priority. i don't do well at my job, my family does not eat, or bills do not get paid. a four year old's tantrum has no business jeopardizing that. she is old enough to know better. please please please don't waste any time worrying about how you handled this. i'm still wondering at what point you could possibly conceive that you were too harsh.....
at some point the child has to understand they don't control the universe. it's not harsh. it's reality. would you really have spent an extra 15 or 20 minutes making her feel better about throwing a tantrum and throwing a wrench in your already crazy morning? let yourself be late to work? just to ease your guilt? she misbehaved. there are consequences. no guilt mama!