Hello Metamorph, welcome to the forum.
Here are my answers to your questions:
1)You will only need to do the candida diet for a few months to 18 months to completely heal; the timespan differs depending on how ill you are with it. I have done the diet for 4 solid months now and I am starting to eat more regular foods slowly.
2)Candida is a major epidemic problem; its hard to quantify how many people are ill with it, but almost anyone that has taken large amounts of antibiotics sometime in their life could possibly have an imbalance and are susceptible.
3)Has nothing to do with genetics, more with lifestyle and diet. I wouldn’t worry about your genes…
4)Brush your teeth more or try the oil pulling (see the oral thrush post and do a search for it).
5)It is possible for it to be transmitted, if you both do the oil pulling beforehand then there is much less of a chance of anything being transferred. I wouldn’t worry about it too much; if you both have weak immune systems then you both could possibly have candida. If she has a strong immune system, then I wouldn’t worry as much. This is something that hasn’t been researched but just more of an unsubstantiated rumor/situation that is hard to verify scientifically. There are stories out there, but it’d be more common if it was easily transmitted.
Suggestion for her digestion problems: chew your food 20-30 times per each bite, this is how much you need to chew your food for proper digestion.