Preeclampsia isn't really related to diet or exercise, so far as we can tell -- but it is related to obesity.
This likely means one of two things: obesity unmasks a tendency to be carrying the genes for preeclampsia (remember, an awful lot of obese women do *not* get preeclampsia), or obesity triggers underlying conditions that raise risk of preeclampsia, like insulin resistance.
Even skinny women can be insulin-resistant; to a great extent the tendency to gain weight in the abdomen rather than the hips (the "apple-shaped" body instead of the "pear-shaped" body) is a phenotype programmed in utero -- so while you were developing in utero. Women can be a normal weight, or even underweight, with that tendency to gain weight in the waist and an inclination towards insulin resistance.
