My condolences on your loss.
A tradition that my family has for the passing of a family member might help you and you sister.
Gather pictures, art, clothes, cookie cutters, holiday decorations, letters, gardening tools,
basically anything that contains a story of who your mom was, what did she like, how she lived her life
then gather friends and family, just two or ten, or as many that will come, begin to tell the small stories of her life, how she made meals, how she kept her garden, what music she liked, go until the stories fill you with her life, until the grief is displaced for a while.
Leave the objects displayed, look and remember the connected stories so when grief overwhelms, some small item will trigger a smile, a memory, a tale
their story is our legacy, the base form which our stories begin
We, your many friends here, know she started a great story and teller of stories in you.