My husband went to Japan a few years back with his reserve unit. He neither spoke nor wrote one lick of Japanese, yet he managed to take a trip to Mount Fuji all by himself. He had a blast. Got off on the wrong station and had to figure out "what now?" He said that he did a lot of pointing and shoulder shrugging and that method of communication got him back on track. lol
He also managed to take a picture of Tokyo and there was not a single person in the picture - it could have been Frankfurt except for the writing on the buildings. How he managed THAT I have no idea because he told me about the wall of people and that once you are in that mass, you have to move with it.
He told me that he wasn't too keen on the food. When I asked him what he had eaten, he gave me a long list of odd foods. I think I would have thrown in the towel LONG before he did. Having an open mind and an adventurous spirit helps a lot and you have lots of time to get prepared for the culture.
Your mom is just worried. Japan is a long way away and she couldn't come to the rescue IF anything went wrong. But NOTHING WILL, so she needs to relax.