T.H.
It is not necessary and in fact, I'd almost be surprised if those envelopes were sent home by the school. Most churches have those envelopes in accessible places for parishoners to pick up and use, and kids are notorious for just taking stuff like that, they just like to pick things up. Could it be that she just grabbed some while walking the halls or something and they were in her backpack? I would participate in the preschool fundraisers but you are in no way obligated to do anything else especially if you do not attend the church there.