Just clarify.......are you saying that she is post-op?
Hmmm depends what you consider"adult-rated" images. Pics of breast development or the shrinking of male genitalia would probably be innocent enough.
The thing is that firstly I do not know what hormones and blockers your g/f is taking and for how long, but the hormone regime for MtF's tends to suppress sexual motivation and activity.
You said "sent adult rated images to some friends" I note the plural, which suggests that the pics were not sent as part of an affair.
It's not unusual for an MtF to want to show her changing and developing body - I did it myself once I was post-op, sent some very racy poses.
But if you are saying that your g/f sent pics of actual sexual activity ........ that seems not at all good.
To be honest, no-one truly knows anyone else's motivations for sure, even when you have all the facts and know them personally.
Female to males very often feel very horny all the time because of they are put on high levels of testosterone. Presumably they adjust after a while.
MtF hormones tend to suppress sexuality, except for one scenario - if a person is started on Decapeptyl or Zoladex injections, for a week to ten days after the first dose they have a huge testosterone spike and are probably recklessly horny. The clinician usually counters this by prescribing a strong anti-androgen pill for those first ten days.
I doubt that there is a hormonal reason of excuse in your g/f case. You are in the USA I think? From what I gather, people in the USA use Spironolactone as an anti-androgen.
I think that your problem is more likely relationship/personality based rather than directly hormonal - your girlfriend either :-
1) Did not realise that you would care if she sent such pics (that's not good, she does not understand you, so you two need to talk)
2) Sent them anyway because she does not care if you know and how you feel (very bad ...... you may well be in the wrong relationship)
3) Sent them aware that you might not approve but expecting you to never know (...which really is little better than #2)
Post another four replies here....... just go to some random threads, pick up the gist and post a relevant one-line reply, and I will Approve them so that the PM system becomes available to you. (You will know when that is because when you click on my Profile, there will be an option in the lower left to contact me by PM )