I mean, everything is gay and trans, like that's just a fact. Anyway. How did she become a Spartan?
She was one of the last batches of kids sent to off world schools from Reach a year before it was glassed, and with no where else to go they put her in the Spartan program to see how she performed.
Because she was quiet and never snapped back during early training, she was seen as a prime candidate for the next step.
Before that next step is when she came out to her superior officer, expecting it to disqualify her, unfortunately for her it wasn’t a disqualification but an opportunity to see how this process could effect her further.
They gave her the go ahead on both transitioning and the Spartan process at the same time, she was - and continues to be - met with mixed emotions by this choice on the UNSC’s part.