As harsh as it may seem; I would stop answering her calls during the day. Call her back if necessary, and say "Oh, sorry; I was busy with the kids. Is there an emergency?" and so on. I would not cater to this any more. She does it because you have allowed it so far, but this is a little ridiculous. Especially seeing as you are providing daily reports as it is. And for a 3 1/2 year old!!
If you end up losing this family, I would say that it was inevitable. This is exactly the type of person that no care arrangement will ever be good enough for them. Good riddance!