They are used to my occult ways of communicating with spirits, so I’m comfortable doing it.

What do you mean by the spirit here? The soul? Most people think that the spirit is unseen. You mean are you talking to the dead?

I could doubt myself a million times over this strange encounter, whether it was truly her grandmother or not

If we asked the Bible about it, for sure the answer is No. It's not her grandmother.

Anyway, we have different belief but anyway, you're right, take what is good.