I hereby declare this MY definitive Susan Pevensie answer:
"What happened to Susan in The Last Battle and why didn't she go to Narnia?"
Susan didn’t go back in the last book because she wasn’t on the train with everyone else and what happened to them on the train didn’t happen to her, because she wasn’t with them.
And who knows? Maybe Susan grew up, and had lots of adventures and lived a long long life. But children’s books are about children, not…
“Susan left school and became an electrician, and taught six apprentices, and formed a construction company and spent two months a year building schools in the mountains of South America, and once she single-handedly brought a dozen goats to a village so that they’d have milk for the children. And then she retired young and became a painter, and took the money that her paintings sold for and started an art-and-literacy program for grownups who had never learned to do one or the other (or both) when they were at school. When her eyes got bad, she taught herself to knit in the dark, and made teeny tiny baby hats for the hospitals, and sat with the babies whose mothers were addicted to drugs while the wee things cried and screamed. And finally one night when she was nearly a hundred years old, she went to bed in England and woke up in Narnia.”
"What happened to Susan in The Last Battle and why didn't she go to Narnia?"
Susan didn’t go back in the last book because she wasn’t on the train with everyone else and what happened to them on the train didn’t happen to her, because she wasn’t with them.
And who knows? Maybe Susan grew up, and had lots of adventures and lived a long long life. But children’s books are about children, not…
“Susan left school and became an electrician, and taught six apprentices, and formed a construction company and spent two months a year building schools in the mountains of South America, and once she single-handedly brought a dozen goats to a village so that they’d have milk for the children. And then she retired young and became a painter, and took the money that her paintings sold for and started an art-and-literacy program for grownups who had never learned to do one or the other (or both) when they were at school. When her eyes got bad, she taught herself to knit in the dark, and made teeny tiny baby hats for the hospitals, and sat with the babies whose mothers were addicted to drugs while the wee things cried and screamed. And finally one night when she was nearly a hundred years old, she went to bed in England and woke up in Narnia.”