Overall appearance
1. looks female with clothes on, or even when topless; average height and below-average but still healthy weight for a girl her age; considered an attractive girl by multiple characters
2. has small breasts (not specifically said to be small because of her IS condition, but could be)
If it matters, she's white, with light skin and black hair.
Details that matter to the plot
3. has an erectile phallus large enough for intercourse; external anatomy otherwise closer to typically female (not described in detail)
4. definite female gender identity, but with no desire to change her body; lesbian
5. was not atypically late in reaching puberty
6. possibility of "normalizing" surgery was brought up at birth (in 1996), meaning she was identifiably intersex at birth; there was no actual health reason for surgery; her mother got to make the decision, did some research, and decided against it
7. no incapacitating health problems; physically and mentally qualified to fly a highly maneuverable aircraft
And these other details are mentioned but would be easy to change.
8. said to have no testes (not even internally) and not produce sperm
9. implied she ejaculates like a male (I'm thinking about removing this implication regardless, but even if it goes unmentioned I should probably still know whether she would)
(8 and 9 are not inherently contradictory, since sperm is actually a minority component in semen; but I have no idea if there's an IS condition that involves this combination.)
I guess that's it. I haven't written anything that specifies her chromosomes, whether she can become pregnant, or anything else about her internal anatomy; this is because those aren't the kind of detail I'd mention for a reason other than to specify her condition. And no IS-related health problems are currently mentioned, but that's easily changed if necessary.
So is there anything that's consistent with what I've said? And if there's something that's close but doesn't quite fit, which of the details that I mentioned would I need to change if I wanted to make it that?