My very dear friend's Mother just died. I would use the term past away but I just can't bring myself to phrase it that way. That is probably because I worked in the funeral industry for years and heard all kinds of phrasiology for death.
Not physically being able to attend to her Mother's memorial service is very painful for her as it would be for any of us. My advice to my friend was to write a letter to her Mother about her feelings.
We all have been faced with this reality and the loss of any loved one is hard and complex in the way we face it. Along with the stages of grief is the need to have closure and that is different for each of us. Some are able to move through and beyond grief quickly while others have a more difficult road to hoe when it comes to letting go. All are acceptable and needed, it just depends on where the mourner is at that time.
I have found in my 6 decades on this planet, that in order for me to shut the door on painful situations, I have a need to write my feelings down and then let the feelings go. I know this technique does not work for everyone but I have always found comfort in seeing the "hurt" in words and then either burning it, shredding it or in some cases mailing it to myself (this technique gives me time to let go).
Advise is not directive. When something has worked for me, I pass that information forward in hopes that I can spare someone else discomfort. It may not be what works for you but peace is something we all seek.