Hi Elsa,
In all seriousness, I personally feel it's time to visit the therapist. I'm inclined to think this is another form of denial, manifesting itself in a form of uncontrollable desire. If it continues without professional attention, it could lead to further 'unacceptble' behaviour, with regrettable consequences.
Not understanding what your term "fun" means; if it's excessive and consistant, it may be a smoke screen for other issues. I may be going totally over board and be 1000% completely wrong on all counts. However from what you've said and the reaction from others' comments, my alarm bells are starting to ring.
After 5 years of HRT, does she have any plans for further transition? Is she becoming withdrawn? Are other friends dropping off? Is she saying or carrying out any other irrational behaviour? If there is a "Yes" to any of those questions, apart from transition plans, then yes; medical intervention is a necessity in order to maintain a healthy well 'balanced' transitioning lifestyle.
It may be something very simple, and she just wants to make a statement, It can also be an indicator of something deeper.
You are currently in a very good position to guide her towards a healthy outcome. Do your best not to alarm anyone over it. Just be supportive of helping her find a professional solution. Keep all your local emergency numbers at hand, (police, ambulance, suicide help line, emergency mental health) ready for immediate use, and contact her on a daily basis over the phone to ensure her safety and so you can determine whether her condition is deteriorating at all.
Just stick with her. You never know when you may need, her.
Keep in touch and let us know how you are coping.
Be safe, well and happy
Lotsa huggs
Catherine