My mother in law has been back on hospice since early March. She is constantly moaning and saying please help and have mercy. How to cope?

Not discounting anything that anyone else has said. But I have been in hospitals and NH where patients have done this around the clock and I was told they were not in pain. It was very difficult to witness and it wasn’t my loved one. I would not hesitate to contact hospice for assistance and perhaps consider a diff hospice if this one is not supportive.
I am so sorry. I hope you and your MIL find relief soon.

Maybe hospice is not the right solution for her. Maybe she really can't cope.
I'm sorry, I don't want to make you feel bad, at all, I just put myself in her shoes, it must be very hard to be in that position.

Is she religious? If yes have you tried reading scripture to her?

I would try that 1st and if it doesn't calm her ask hospice if they can help calm her.

I would have a difficult time coping if my LO was moaning and begging for mercy. Sounds like she is in a lot of pain, notify Hospice and make them aware, they may have to bump up her medication to make her more comfortable. I used Hospice services for my dad and brother, both were comfortable and free from pain, no moaning what so ever. Please take care of this ASAP. It appears she is suffering greatly. Hope this is solved soon.