I second what everyone was saying before- I am an only daughter (not an only child, though), and my mum gets upset, I think, every time we speak on the phone. I cannot say for sure, because I don't see her, but towards the end it sounds very much so.
She is not that happy with us living here, so far away, and since our children are four out of her five grandchildren, it makes it even harder.
But- there are lots of memories, and she saw the kids growing up, so we had very good times together..., and I think those memories are really important. I would also go and visit, she will remember the good times you had and she will remember this last visit, too..., until you are meeting again on the other side of the world!
Just make sure you have a safe trip, Sophie's advice re train sounds quite reasonable to me!