After all they were the two people she technically cared the most about- one is her only blood related relative and her father, and the other is the person she loved to the point to becoming mad and evil in her past life.
But yeah I still wanted to see a cold and indifferent to all FL
Her grandfather and her much younger "aunt". Are also her blood relatives and her grandfather before he died made more of an effort to help in the 2nd life and didnt wrong her to the extent FL's "father" did.
Her grandfather is dead. The aunt is not a blood relative (though still a relative and I don't mean to say blood relationships are everything/superior)
The only other blood relative is probably her brother who is technically her cousin.
Also a parent is different to grandparents/other relatives. People more likely to forgive their parents than other relatives for the same action. Or at least that's what I think.
There's also a matter of time and people. The grandfather made an effort that's why FL accepted her way earlier than her father. Unfortunately he died too soon. If he were still alive, I have no doubt FL would treat him kindly (maybe in a tsundere way or maybe normally but still kindly). Also FL was still adjusting to being loved and cared for when the gramps was still alive. She didn't know how to feel about it or how to react to it. On the other hand, now it's been years since FL experienced the love and care from others. She's more able to care about others since she's being cared for too.
The daughter of the grandfather is her aunt and blood relative. The father and the husband were responsible for inflicting the most trauma on the FL yet she open herself quickest to them.
She acts so cold and indifferent to everyone especially those who care about her and have proven themselves yet for the ML and her father the two deserve the cold treatment the most she easily waivers.