Welcome to the forum! Great ppl here!
It is not uncommon for loved one's to visit after they have passed away, even if you didn't get along. September 23,2008 my BF and I got into a fight we broke up, I told him to drop dead on the 24. The next day he passed away (drowned) all that hate I had for him disappeared, that night in my dream he came to me as real as I am doing this said I am so sorry for what I done. I snapped awake. Anyways when a loved one has passed they may not be at rest cause unfinished business.
If I were you write a letter to the person, read it out loud then tell the person I forgive you for the bad times we had shared and I love you no matter what. Then tell them to pass on that everything will be fine .