Looking at this thread I wonder what can it teach me? When you say you wanted to thank your Grandma for what she meant for your life, it has me thinking about someone who lives out of my reach, and whom I'd like to thank for the positive impact this someone had on my life without possibly ever realising it.
I wonder whether or not I should simply write this person, cause when I read your post I wonder why you didn't simply write your Grandma or phone her and tell her how much she meant to you and sent her the present meant for her without waiting for Christmas to come by, or sent her presents every other day for that matter.
There's no need to thank people face to face on one special day you wait for, or to wait to be reunited with them in the flesh, when you've got a chance to express your feelings right now.
When I read your post I feel you're grieving over the loss of a chance to express your love to your Grandma fully when there was time much more than missing out on celebrating Xmas with her or that LoA seems to have failed you.
LoA isn't a substitute for living life in the present. If you feel like expressing gratitude and love do so right now in whatever ways possible. Same goes for all other areas of your life. Then when death comes - and not even LoA can prevent that - you have closure.
To master the astral planes when you haven't mastered how to live in the physical one to the fullest is a fruitless effort. It makes little sense to try to move an object with your mind when you have hands to move it. Likewise if you want to talk to someone you haven't seen in a while, don't try to use LoA to make it happen, but pick up the phone.
LoA is a Universal Law, it is part of the design of the Universe and it doesn't fail. And no, you still don't always get the results your ego had in mind, but that doesn't prove a limitation of an Universal law, but just the limitation of your mind and your ability to control the Universe or yourself. If this causes you unhappiness then let go.
You still got your own hands to rely on to make things work for you in the physical world and that was enough for generations who'd never heard of LoA to get by on. Their own hands and faith in God and themselves. You don't need to believe in LoA or know how to apply its principles to lead a happy, fulfilled life. Don't think about it, just do it.