That is hard- I have a co-worker in a similar situation, only with her son's daughter (he has custody).
Do not coddle. Do not do favors. Tough love now will (hopefully) make her "use" you more politely. She needs to grow up. It is really, really unfortunate that there is a child involved in the middle of this adolescent temper tantrum. But, you can't help your grandchild if your daughter is determined to use her to get what she wants. It's not good for anyone involved, not even your grandchild. If she is really neglectful can you get DSS involved?
Do not coddle. Do not do favors. Tough love now will (hopefully) make her "use" you more politely. She needs to grow up. It is really, really unfortunate that there is a child involved in the middle of this adolescent temper tantrum. But, you can't help your grandchild if your daughter is determined to use her to get what she wants. It's not good for anyone involved, not even your grandchild. If she is really neglectful can you get DSS involved?