Its not unusual here in Thailand for tgs to not have bottom surgeries (srs). Many feel that they may lose the ability to orgasm, and lose their sex drive. Many have been on some sort of HRT program for many years. From my many discussions with my tg friends, here, who still have a penis and take E, they continue to have the abilty for erections and have a great sex life. They go off E sometimes with no negative effect.
Longterm damage, from E, to the liver should not be a problem if carefully monitored. Many of the liver issues are caused by excessive alcoho, especiallyl when on meds. Also self prescription of E in large doses is not advisable. Use a Doctor and take a blood test To monitor the liver and kidneys every 6 months for the fist few years and then yearly after is advisible.
Generally speaking if you are a sexully active and healthy male, then the E will not stop you from erections. Many Western tgs regard their penis with disdain and taking HRT confirms their view of who they are without a penis, which they hate, this mindset will lose their ability for erection. As you are on HRT for longer then your new female mind will have different triggers for arousal and you will mentally change and adapt.
I was on HRT for 3.5 years before srs. I was sexually very active and never had a problem with erection, just a different trigger mindset to get there. Maybe this mindset allowed me to orgasm easily as a female post srs. Not all people are interested in sex but this is a major concern for younger transitioners.
Finally, I note that she has not started HRT. Well the mental outlook will change on HRT and she may change her view on srs. Read about the effects of HRT mentally on many posts in this forum.