I am so sorry your sister doesn't appreciate how much you want to see your father. Does he have dementia? I can't know what's in your sister's head, so it's hard to guess why she is vague about it.

Could you call her again about it, reminding her he does recognize you two and is happy to see you, and how much you want to go?

I'm wondering how far away he is and whether you might be able to arrange alternate transportation--maybe through a friend or a taxi--if she won't take you at all.