A friend’s daughter/son is transgender and never had a problem with public bathrooms as an adult. Just uses the stall with the door. If there is only one, he just waits until one is available.
The person is either a daughter or a son. I’m presuming the former here.
“A friend’s daughter/son is transgender...”
Your friend doesn’t have a daughter/son. He (or she) has a daughter OR son who doesn’t seem to have enough brains to know what sex they are (in spite of that big hint between their legs).
If it has a "y" chromosome, it is male down to the very last cell. Insanity should not be indulged by referring to a mentally ill male as "she" or "her." It is not female in any sense of the concept.