life's scarey....but you don't get to control other people's plans ( by inserting yourself or other ways) because of it. Mary is very rude. The OP is not at all rude.
When I was in my 40's I traveled to Philly for the 1st time - from Buffalo to NYC to Philly by myself. The first time I was met by my friend, the next time I had to get from the greyhound station in Buffalo to the NYC port Authority station to Philly's 10th st station, and then deal with the SEPTA system - alone. I got directions and still got horribly lost. Got off on the wrong stop and ended up walking around 52nd to 54th streets around dusk...the cops stopped to make sure what the heck I was doing there - finding I was lost and from out of town, they had a laugh and got me on the right bus and I made it to the school my friend was at....in NW Philly.
Was I scared? Heck yeah, but at some point I realized that my life would be immeasurably better if I could deal with that fear and go past it...Mary is not doing that..she's trying to limit other folks because of her fear. Mary can deal with it or not - but she does not get to insert herself or limit other people's freedoms because she has this fear.
If I had to treat a fellow adult as a child and either walk them through a train ride or not do things because of them, means that this person has gone from a companion to a dependent...I don't need that and I would be limiting what I do with them to things they can handle on their own. I like the idea of Mary paying for a cab, if she can't deal with driving or a train - it puts all the responsibility on Mary.
It would not work for me to have her waiting in a cafe to babysit her on the way home, or to have to painstakingly explain to her how the bus would work,,,,Mary needs to find a way to get around that does not turn another adult into a caretaker. that road leads to resentment.