I'm getting desperate

My girlfriend has really really high blood pressure and has had so for a few years (shes 25). I don't understand it - she eats well, exercises, is young, doesn't smoke, doesn't drink excessively etc. She has a stressful job but I don't think that would result in chronic high blood pressure. And its HIGH.
Of course she's been to the doctor and hospital for checks and all is fine they say. They scanned her kidneys and put her on a BP monitor for 24 hours but so far theres no solutions or reasosn for it. Shes reluctant to go on medication as this may make it difficult to have children (correct?) and is looking for any way at all - no matter how crazy it may seem - to lower her blood pressure. Anyone have any advice or help? Like I say we're getting desperate and its getting her down.