True fears and unwarranted fears may at times feel the same, but you can tell them apart. True fear is a gift that signals us in the presence of danger; thus, it will be based upon something you perceive in your environment or your circumstance. Unwarranted fear or worry will always be based upon something in your imagination or your memory.
Worry is the fear we manufacture; it is a choice. Conversely, true fear is involuntary; it will come and get our attention if necessary. But if a parent or a child feels fear constantly, there is no signal left for when it's really needed. Thus, the parent who chooses to worry all the time or who invests unwarranted fears into children is actually making them less safe. Worry is not a precaution; it is the opposite because it delays and discourages constructive action.
I suggest working to increase your level of comfort about the school, but at the same time, working to reduce unwarranted worry in your life (and thus, in your daughter's life). You may want to check out this link about reducing worry.