No way would I plan to travel 4 hours away when I was 36 weeks pregnant. I had to get my Ob's approval to travel 2 hours away at 35 weeks and he only said it was ok a week prior! Your Mum could plan the whole thing only to have your Ob say that it wasn't safe to travel. And what would happen if you had bub while you were there? Is there a hospital there that can manage a 36 week bubba? That was my issue - that the hospital near where I went was only able to deal with bubbas past 37 weeks so 35 weeks was too early. Of course, I didn't actually go into labour while I was away, but I had to consider it.
Don't let your worry about your Gran traveling 4 hours each way trouble you. She's a big girl and she can make her own decisions. If she can't come, then she can't come.
I planned both of mine on days that suited me, in locations that suited me. I struggled through my first one as I'd just finished work & I was tired & grumpy. I didn't enjoy it so it sort of defeated the purpose. The 2nd one was SO much better.