Hi - first of all I want to congratulate you on taking matters into your own hands, and making the logical connections with nutrition. We're told so often that food doesn't cause Acne or rosacea, and I know that at your age I had no idea I could question what the Drs told me!
I don't know the answer to your question about liver toxicity in your late teens, I'd be more likely to assume that it's hormonal. Having said that, I'm 29 and I'm about to do a parasite, liver and Bowel Cleanse in the hope of clearing up my rosacea and slight acne, and I do think that my liver is causing those problems as I'm now getting other symptoms that make me think it isn't working properly.
Over the past years I've found that the best way to keep it under control was to cut out dairy altogether. For me, there's a really direct connection between dairy and acne/rosacea, so rather than intricate diets, you might want to try cutting out just dairy, or just Sugar and wheat bread/pasta, one at a time, and see if that helps. As a long term solution it might be more manageable.
Good luck with whatever you decide to do. I'm sorry I'm not more helpful, but if you want I can let you know how my cleanses go.
Also, someone on the colon hydrotherapy board might be able to suggest a practitioner in your area.