It's my hunch that what your mum said was just a misunderstanding. When you said you wouldn't go to the KH service she maybe thought that you didn't want to see any JW's at all and that's why she suggested visiting on the friday with other non-JW friends of the family. I don't think it's worth falling out over.
My mother said something similar when my grandad died and they were having a memorial at the KH. She asked if I was going to attend or if I didn't want to bother and just go to the crematorium and pay my respects (not even sure how that would work). She asked it in a way that said she thought I had made up my mind not to go and that it didn't really matter to the family anyway. I did go of course and everything was fine in the end. It was just a misunderstanding in that my mother thought that I didn't want to see or speak to any JW's. She was extending the ludicrous JW rule of shunning on behalf of me against them even though I had no personal grievance with anyone and I wasn't even DA'd or DF'd.
Anyway I'm sure everything will turn out ok.