First, let me offer my sympathy to you. In today's world, you are young to have lost your mother. But it is never easy at any age. The people you consulted are probably correct in saying there are no books on death written for your daughter's age level. If you had asked me, I would have had to say the same thing. But, you didn't ask the person who is probably more knowledgeable than the rest of us: the librarian in the children's section of your public library. Chances are she will know of an appropriate book. Certainly there are several beautiful ones written for slightly older children, many of which approach death by depicting the death of a beloved pet.
What we tell children of any age about death will be influenced by the family's religious beliefs, so it is good that you discussed it with your minister. It is never easy, and one discussion won't take care of questions for all time. Finally, I would suggest that you show pictures of your mother to your daughter from time to time and help keep her memory alive.
Our parenting advice is given as suggestions only. We recommend you also consult your healthcare provider, and urge you to contact them immediately if your question is urgent or about a medical condition.