Death in dreams only means change or the ending of a certain thing in ones life. Only you can really interpret your own dreams but I can give you something to think about.

Is your mom going into a new career, having another baby, getting remarried????.. anything in her life that is changing which makes the old way of her doing something ending? Think about that.

Death is actually good in a dream when it's not precognitive (and in your case I'm positive it's not but it wouldn't hurt to tell your mom to be careful crossing the street.

Food: you both were eating in the dream before the accidental death right? What does food mean to you? Nourishment, comfort? Link that to the symbol of Death (something ending to something new can begin).

I hope this helps.

Blissful