I don't think you should go. Can you have your own family memorial service?
My MIL was abusive to me and our children throughout my DH three years of living with cancer, she wanted him to go and live with her so he could be looked after properly, she told the Macmillan nurse that he would be better off living with her as she had fully fitted carpets!
She made official complaints about the hospice, as they hadn't informed her of stuff, what with her not being the next of kin, she was bitter, it ended up for the last 9 weeks of my DHs life all visits by his family to our house were supervised by the oncology social workers, (there were three incident reports about her behaviour from the agency carers already).
she put in complaints about them too, and the agency carers.
she phoned the oncology consultant and told her I'd been beating him as he had purple marks on his arms, Dr explained that it was due to his medication, the kids disability social worker was complained about, and was investigated as he didn't return her calls, due to the abuse she gave him.
But when DH died I did let them know the funeral details, because my DH wanted them there, we had 2 bouncers at the funeral, true to form MIL stood up during the service shouting and swearing at me. They wouldn't let us out the doors, we had to leave by the other door, the hearse had to reverse up to us, still they were shouting and swearing.
This was all done in front of our three children who have autism, 8 years on and they are still upset about it. That was the last time they saw them.
We have had no contact since and never will.
If I could rewind I wouldn't have invited them, I did it as it was what DH wanted, he was mostly unaware of their behaviour due to his brain tumour.
MIL got the guy who did the funeral to later do a family memorial service, I know this as he rang me to ask if they could borrow the ashes, funnily enough our children had not been invited.
Now to anyone who met MIL they would hear about her evil DIL