Hi Ganesh
I presume the travel insurance policy you have is an annual family travel and your daughter is under the age of 18?
If she is travelling with just the school, ie not travelling with either of her parents, it is probable that her trip would not be covered by that annual travel policy. You are best to phone them to double check this, if they provide good cover they may already cover it, or will be able to cover the trip on an advised basis. If they cant you may just need to take out a single trip policy for your daughter for that one trip, it wont be much, possibly £10 online.
Hope that helps