As for your mother’s friend – it sounds like she started planning this celebration of life service before she discussed it with you and your sisters. There is nothing wrong with having more than one service with different guest lists even if some people are invited to both. However, since your mother just passed and you have not yet had the memorial service for her this person should not have done this without asking you and your sisters first.

I think the best thing to do at this point is to call her and simply ask her to hold off on her plans (don’t send the invitations) until you have had your private gathering to honor your mother. (I assume your plans have been announced to those included.) I wouldn’t worry about the people who will be invited to both services – these were close friends of your mother’s and will certainly be there for you and your sisters as you deal with her loss.

It sounds like your mother was a wonderful person to have so many friends who want to celebrate her life, and I hope that will also bring you comfort knowing she was loved by so many.