No, I don't think it's about being transgender. I can see why you might, but it says that her mother said she couldn't love the physical way a woman SHOULD. If it had been could, I would say that makes a pretty good case for it being about someone transgendered, but the use of the word 'should' implies that she can't love the physical way that SHE should. You wouldn't tell a boy that he can't behave the way a woman should -- it just doesn't make sense.
No, I don't think it's about being transgender. I can see why you might, but it says that her mother said she couldn't love the physical way a woman SHOULD. If it had been could, I would say that makes a pretty good case for it being about someone transgendered, but the use of the word 'should' implies that she can't love the physical way that SHE should. You wouldn't tell a boy that he can't behave the way a woman should -- it just doesn't make sense.