J.B.
I think two weeks before sounds good. My MIL (who I passed away before I met my husband) died in late March. Within 10 days of her death are my two oldest sons' birthdays and my grandmother-in-law's birthday (my MIL's MIL). I wasn't there for the first anniversary, but we do go to a memorial service at temple near the date of her death and then sometimes end up celebrating the birthdays the same day. For my FIL, having grandkids around and seeing his own mom still living a great life and celebrating another birthday (she's 92!) takes away some of the pain of the day and reminds him that life is still good. Hopefully after this first year, which I would imagine is the hardest, it will be easier to celebrate closer to her actual day.