I don't want to meet my transgender grandmother for the first time
Why don't you want to meet your grandmother?
I just don't want to see her, I can't explain why.
If you are uncomfortable meeting your grandmother for the first time, that is understandable. It can make people nervous to meet someone new. But you should try to be courteous and accepting, regardless of your nervousness.
I don't need to care about her. I'm not planning on seeing her again.
If you don't want a relationship with her, that is fine but you need to tell her. And if you don't want to meet her because she is trans, you should look into that as well.