Call me old fashioned. There are two genders determined by chromosome combinations, XX female and XY male. Pronouns are not interchangeable. He, she, not they, them. Used in a sentence: Here is a picture of Kate Upton. She is a model. She is the appropriate pronoun.

It would be appropriate to use them when referring to Kate. Such as: “Wow, Look at them!”
That just shows there are exceptions to every rule.