There are excellent vaccines for Hepatatis A. If you haven't been vaccinated, then this is very important, regardless of whether you go camping or not. Hep A is fecal transmitted, which means also transmitted by hands of people who don't wash after defecating. Hep A is endemic in Mexico and Central America and much of our fresh fruit and vegetables comes from there, as well as from farms in the US using immigrants from Mexico/Central America. Obviously, workers in the fields on these farms seldom have the opportunity to wash up after defecating. Bottom line, you can get Hep A just by touching a piece of fresh fruit in the supermarket and then eating something later without washing your hands first, even something other than the fruit, since the germs from merely touching the fruit would still be on your hands.
I don't know why your sister got so sick from Hep A. I thought it only lasted a month or so. Hep B is much more serious. It is common to be knocked down for a year with that. And if you get the aggravated form of Hep B (namely, Hep D) then you'll likely die. Hep C is also bad knews. Hep B is blood born--mainly drug addicts, homosexuals and health workers are at risk. There is an excellent vaccine available. Hep C is poorly understood. Mainly drug addicts and criminals get it. Probably blood borne for people with weak immune system. No vaccine avail. Kills you after about 20 years without symptoms.
I've been drinking untreated water from highland streams for years, even when I knew there were animals (sheep, cows, horses, goats plus all the wild beast) crapping in the water upstream. The main danger here is strains of e.coli, since I couldn't care less about giardia or crypto. Humans will eventually adapt to most of these strains of e.coli, as I understand, but the initial shock could kill someone with a weak immune system. That is why keeping the immune system strong is vital, especially for long-distance hikers. DON'T PUSH YOURSELF TOO HARD!!!! And take a daily Vitamin supplement and eat some boiled or fresh nettles daily if you can find them.
The main thing that worries me about untreated water is liver flukes. I read about somewhere that these are common in in lowland streams. People who eat watercress salads, for example, are prone to getting liver flukes. I would never drink directly from lowland streams.
Water from the surface of quiet mountain tarns in the mid-summer is usually pure, since the intense ultraviolet light at high altitudes is a strong germicide.