this is something my mom always used to point out; that you can grieve loosing someone whenever and wherever you are. just like you can believe in religion "X" whenever and wherever you are, and not just Sunday mornings in a church (I'm not religious, but I think this is a big concept to understand). she for example isn't physically able to go to the graves of people she has lost in her life (moved) but this doesnt' mean she can't grieve their loss or remember them in some way... something like a flower or a sunny day or a certain meal might trigger her to make the connection,.... I don't know if this makes sense. but it's nice to see that you can remember someone without sadness all the time and that you can do so whenever you feel the need to....I usually put so much emphasis on the actual death date. I am trying to remember that it is just a calendar date and I can remember her or visit her any time I want
I have a horrible time w/ death dates of people who I have lost in my life too, none of them like your loss I would imagine, but my point is when those dates come around, I almost feel obligated in some weird way to be sad that day and expect this tragedy to happen (as you said)... but if I think about it, that doesn't make any sense. it won't bring them back to life if I choose to be miserable that day. If I am miserable then that's one thing but expecting to be so is almost like a self-fulfilling prophesy... I think it's okay to be "okay" on that date. you know you love your sister and you know you miss her. you don't need some kind of technical thing (date, time, calendar etc.) to know this. just like she's always with you wherever you go and always a part of you no matter what.