Wonderful thought experiment. I’d like to tackle the second hypothetical, a person from a hundred years ago.
I think that we as human beings have a supreme capacity to be underwhelmed. If aliens landed on planet earth 🌍 tomorrow, by next week we would accept that as the new reality. I think of all of the science fiction type gadgets that have come into reality in my lifetime: Star Trek communicators and Dick Tracy TV communicator wrist watches (smartphones), inter-galaxy travel (Voyager), exploration of Mars (Rovers), computers from around the world talking to each other (the Internet), genetic cloning of animals, TASER, lasers, electric cars.
If our time traveler could accept that what she saw was the natural progression of technology, then acceptance of it shouldn’t be a long-term issue. And if they can access the information technology, they could literally Google everything that confused them.
(By contrast, someone from Ancient Greece or the Middle Ages would see it all as magic of the gods or witchcraft, and their brains would probably explode.)
Where I see the greatest challenge for our time traveler from 1900 is that she will have limited employable skills. In 1900, most people lived in rural areas and half the population worked on farms. Not being computer literate would limit her options in 2020. Conceivably, she might have had a higher quality of life if she had stayed back in 1900.