A person’s gender is always valid. Even if you don’t understand.
When we we use pronouns like “she” or “he” to identify a person, we might be making an assumption about that person’s gender that differs from their preferred gender identity. Some people express their gender identity ambiguously, meaning you might not know which pronoun to use just by looking at them and have to make an assumption. For other people, appearances can be deceiving– even people who clearly look to be one gender may identify as a different gender than you would assume. When someone has a different gender identity than you would assume that means a different pronoun.